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decont046_final report rev5a.doc
LP GAS CONTAMINATION REMEDIATION AT BULK TERMINALS PROJECT
FINAL REPORT
Prepared for the
Propane Education & Research Council (PERC Docket #11649)
August 18, 2006
By: Nolan Sambrano, Jared Meyer, and Alex Spataru
ADEPT SCIENCE & TECHNOLOGIES, LLC 51 Rover Boulevard
Los Alamos, NM 87544 USA Telephone: (505) 672-0002
Fax: (505) 672-0003
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Table of Contents
I. Abstract .........................................................................................................3 II. Glossary and Abbreviations...........................................................................3 III. Introduction ................................................................................................4 IV. Residue Testing Methods...........................................................................5 V. First Small Scale Decontamination Test ........................................................6
A. Summary....................................................................................................6 B. Objectives ..................................................................................................6 C. Experimental Set-up and Materials.........................................................6 D. Procedure ...............................................................................................8 E. Results and Discussion............................................................................11 F. Proposed Next Steps ...............................................................................13
VI. Second Small Scale Propane Decontamination Test...............................14 A. Summary..................................................................................................14 B. Objectives ................................................................................................14 C. Experimental Setup and Materials........................................................14 D. Procedure .............................................................................................15 E. Results and Discussion............................................................................17 F. Proposed Next Steps ...............................................................................20
VII. Full Scale Column & Process Design.......................................................20 VIII. Economic Analysis ...................................................................................22 IX. Field Service Recommendations..............................................................23
A. Pre-process Wetting and CO2 Pre-loading...............................................23 B. Flowrate ...................................................................................................23 C. Breakthrough and Activated Carbon Replacement...............................23 D. Filters....................................................................................................23 E. Ethyl Mercaptan Caution..........................................................................24
X. Operating Options........................................................................................24 XI. Conclusions..............................................................................................24 XII. Future work ..............................................................................................25 XIII. Acknowledgements ..................................................................................25 Appendix 1..........................................................................................................27 Appendix 2..........................................................................................................29 Appendix 3..........................................................................................................50 Appendix 4..........................................................................................................53
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I. Abstract Adept Science & Technologies, LLC (ASCENT) has tested activated carbon adsorption columns as a means to remove soluble heavy-end contaminants from LP Gas. Such contaminants lead to operational problems in some LP Gas applications. The composition of such LP Gas contaminants was also determined as part of this project. Process design parameters (i.e. expected flowrates and bed dimensions) were subject to constraints imposed by industry practices (to facilitate subsequent field implementation). Initial results show effective removal of contaminants representative of those commonly found in commercial LP Gas. Also examined was the effect of the process on odorant (i.e. ethyl mercaptan) content. Results are presented along with an assessment of the tested processes. Background information on analytical methods required for these tests is also provided. Follow-on steps are necessary to build on and test commercial applications of this work. II. Glossary and Abbreviations AC Activated carbon ASTM International An international voluntary standards organization Bed-Volume The adsorption column volume occupied by packed activated
carbon or other adsorbent material. Breakthrough Curve A plot of contaminant concentration in the product stream (after
treatment) vs. time (or volume or bed volumes). C20+ Heavy-Ends Refers, in this report, to hydrocarbons with 20 or more carbons
or which boil at or above the boiling point of normal C20H42 per ASTM D2887 simulated distillation, and are the primary component of vaporizer deposits.
CEC Cosmo Engineering Company, based in Japan DOT U.S. Department of Transportation. U.S. Federal agency which
specifies and oversees design and on-road transportation requirements.
DSI Dixie Services, Inc. in Galena Park, TX - the laboratory used for all analytical work in this project
Fines Very small activated carbon particles (carbon dust) which may escape the column.
Heavy-Ends Residue Any soluble LP Gas hydrocarbon impurities larger than pentane. The term includes soluble large organic materials such as phthalates and similar plasticizers and materials extracted from gaskets, sealants, and hoses in LP Gas systems.
micron 1 x 10-6 m (3.9 x 10-5 in). Metric unit equivalent of mesh size used as a rating of filter porosity.
“Special Duty” LP Gas Category term used in ASTM D1835 to identify LP Gas for automotive applications. “Special Duty” specifications are similar to those listed in GPA 2140 (also known as “HD-5”).
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Mixed measurement unit systems are used throughout this report. In some cases, for ease of comparison alternate units are provided, but generally values are reported in units as originally measured or specified. III. Introduction A growing LP Gas industry concern is the effect of heavy-end residues contamination of LP Gas streams on the proper functioning of fueling systems and on other LP Gas distribution system components. Premium quality LP Gas, with low heavy-ends content is costlier and scarcer than most commercially available LP Gas. Sources for such cleaner LP Gas (mainly from natural gas processing as opposed to refineries) are geographically limited in number. This project is to quantify residue content in commercial and/or “Special Duty” LP Gas and to design and test an adsorption column/filtration process to remove “heavy-end” contaminants to make “on-site” a premium quality LP Gas. The goal of subsequent work is to have a commercially viable bulk storage plant heavy-ends decontamination unit. Activated carbon has been tested and used before as a means to lower residue content in LP Gas. One example is a patented process using a packed activated carbon column to effectively remove residual oil while retaining mercaptans.1 Another, a Japanese government funded, multi-million dollar project conducted by Cosmo Engineering Co. (CEC) yielded a 2 ton/h (16 gal/min) demonstration plant to remove residues from LP Gas.2 Principals from both projects were consulted for this work. Petrolane has also used (for a limited period of time ~1980) activated carbon to reduce residues in LP Gas. No data was available for the Petrolane project. To properly address the challenges to remove LP Gas heavy-end contaminants, it is necessary to know what the levels of these residues are likely to be, how they are to be measured, and to what average level they must be consistently reduced. International LP Gas maximum residue limitations (Table 1) provide one measurable and accessible basis to assess the level to which the decontamination unit should reduce the residues content (for current and near-term applications like LP Gas-powered forklift trucks).
Table 1: Summary of LP Gas Residues Limits Nation LP Gas Specification Residues Limit (ppm) Test Method Evaporation
Temp. (°C/°F) US California
HD-5, ASTM D 1835, GPA 2140 HD-10, CCR §2292.6
500 (and oil stain from 0.3 mL of residue-solvent mixture) “
ASTM D 21583 “
38/100
Japan Utility Grade 124 JLPGA-S-05T - Australia ALPGA Automotive Spec. 2000 20 JLPGA-S-05T/86 105/221
Europe EN-589 100 (proposed reduction to 50 ppm limit) EN ISO 13757 105/221
When comparing residues limits, it is essential to note the temperature of the test method used to measure residues content. Methods calling for higher temperatures during evaporation of the LP Gas will drive off more of the lighter compounds (such as gasoline and lighter diesel fuel components), which is likely
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to result in underreporting of the total residue levels and of these lighter heavy-ends. However, these higher temperature methods can adequately indicate the presence of C20+ heavy-ends which are the primary cause of some types of operational problems in applications such as forklifts. As present and near-term applications (forklift trucks, microturbines, and fuel cells) will require cleaner LP Gas to function properly and to meet emissions reduction mandates, it was preliminarily decided that the unit to be designed and tested is to consistently achieve average residues content below 25 ppm in the cleaned LP Gas product (which is over one order of magnitude lower than the current allowable American standards limit). Of note are reported field problems caused by as little as 3 – 10 ppm of “oily residue”. IV. Residue Testing Methods The selection of a suitable residue testing method is crucial to this project. To yield meaningful results, an applicable test method must have repeatable resolution on the order of 10 ppm; be relatively easy and safe to conduct; should require a minimal sample volume; and be reasonably priced. The evaluations of five (5) standard in-use, and near-term proposed pertinent testing methods for use in this project are summarized below:
(1) ASTM D 2158 is the current method prescribed by ASTM D 1835. It was found to underreport total residues, to have undesirably low resolution, and no means to determine residue composition.
(2) Dixie Services Inc. (DSI) P397 provides resolution of 0.1 ppm. Its drawbacks are that it requires a large sample volume and the heating of residues (leading to loss of lighter residues).
(3) EN ISO 13757 reports insufficient repeatability at high resolution, and requires heating of residues.
(4) CEC method5 uses gas chromatography after extraction of residues with a solvent under pressure. The method, currently under review by the D02.H Subcommittee of ASTM, calls for results reported to 0.1 ppm. However, this method currently does not have published repeatability and reproducibility data.
(5) prEN 15470:2006 (E) [previously referred to as CEN/TC19 N 1221 – Annex E] (a proposed replacement for EN ISO 13757), is a gas chromatographic method with results reported to 1 ppm, with 95% repeatability and reproducibility at 20 ppm of 5 ppm and 12 ppm respectively. Heating of residues in this method underreports lighter contaminants. This method is also under preliminary consideration by ASTM Subcommittee D02H.
After evaluating the above test methods, prEN 15470:2006 (E) and the CEC method were considered the most suitable methods for subsequent work. Because of the immediate availability of the necessary equipment, with the advice of DSI, it was decided to use prEN 15470:2006 (E), but with a lower evaporation temperature of 25 °C (77°F) (See Appendix 4 for test method).
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V. First Small Scale Decontamination Test A. Summary
Tests were conducted on one type of activated carbon to treat a liquid phase propane feedstock containing four (4) selected contaminants representative of those previously found in commercial LP Gas. “Propellant grade propane” (~99.6% pure C3H8 with a heavy-ends specification of less than 1 ppm∗ and already processed by molecular sieve media to eliminate water and sulfur) was used as a base to which pure, known contaminants were added. A fifth contaminant, n-octane, was selected as representative of lighter contaminants (such as gasoline-range compounds) which have been problematic in the propellant industry. Two (2) polyester filters of different mesh sizes were placed downstream of the activated carbon to obtain an initial assessment of the amount of effluent activated carbon fines that may be entrained by LP Gas flow through the test vessel.
B. Objectives (1) Determine the effect of a specific type of activated carbon on
removal of selected concentrations of “heavy” contaminants from propane.
(2) Measure effluent activated carbon fines generated at a given process flowrate.
(3) Measure process temperatures and pressures to better predict process conditions (particularly during wetting procedure) in follow-on experiments.
C. Experimental Set-up and Materials 1. Activated Carbon Vessel
A 26.5-in (67.3 cm) long column with an inner diameter of 2.87 in (7.29 cm) [internal cross-sectional area ~0.045 ft2 (41.7cm2)] with removable end caps, and rated for 250 psig (17.2 bar) was designed and constructed (Figure 1). The length of this vessel allows for variation of bed lengths in experiments (ranging from a bed size occupying nearly the full length of the vessel to a shorter one likely to be more representative of the proportions used in a full-scale column). The activated carbon bed length can be shortened by use of additional inert support balls to occupy space. The column was fitted with external pressure and temperature gauges and pressure relief valves. Filter housings were added downstream of the column. The design also includes interior mesh screens which support the column packing materials (inert support balls and adsorbent).
∗ This residue specification is the requirement of the propellant manufacturer for its incoming feedstock propane. The analysis method used by the propellant manufacturer is ASTM 1945 with a modified injection technique using a 4-port liquid valve (Appendix 4).
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a) Vessel b) Filter Stand Setup c) Top Valve, Instrument, and Filter Detail
Figure 1: Pilot Activated Carbon Filter & Experimental Setup
2. Activated Carbon CEC previously developed a metal-impregnated activated carbon designed to remove heavy-ends from LP Gas and which could then be regenerated. This activated carbon mix, because of its precious metal content, was determined to be prohibitively expensive. Three (3) commercially available activated carbons types were obtained for possible use. Of these, a 12 x 40 mesh (1680 x 400 micron) bituminous coal-based granular activated carbon was chosen for initial tests based on its cost effectiveness and reported past effectiveness to remove C12 – C21 range contaminants from LP Gas (where LP Gas storage vessels were contaminated with diesel). Additionally, the activated carbon manufacturer reported that the selected activated carbon may work well to remove heavy-ends contaminants while the removal of sulfur compounds (including ethyl mercaptan) would be negligible. Regeneration or disposal by the activated carbon manufacturer is currently the preferred method to replace the spent adsorbent.
3. Support balls 1/8” (0.318 cm) and 1/4” (0.635 cm) ceramic balls were used to support the activated carbon and to evenly distribute LP Gas flow inside the vessel.
4. Filters 100 micron (149 mesh) x 0.100” (2.54 mm) thick and 5 micron (2500 mesh) x 0.080” (2.03 mm) thick polyester felt filter sheets were cut to fit two (2) modified Impco VFF30 filter housings. The filters were used to asses the approximate size range and amount of effluent activated carbon fines which were entrained during the test.
5. Contaminants The following five (5) compounds (98-99+% pure) were added as contaminants for the feedstock (Table 2).
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Table 2: Description of Added Contaminants for First Test Contaminant Description n-Octane (C8H18): a representative compound of gasoline contamination Pentadecane (C15H32) a representative compound of diesel contamination Methyl linoleate a plasticizer and known LP Gas contaminant Dioctyl adipate a plasticizer and known LP Gas contaminant Butyl benzyl phthalate a plasticizer and known LP Gas contaminant
These contaminants are representative of the type and range of compounds that can be found in commercial LP Gas streams6. Gasoline and diesel contamination can occasionally occur when LP Gas is shipped through multi-product pipelines.
D. Procedure 1. Column Packing
The activated carbon vessel was loaded (from bottom up - the direction of process flow is up) with: (1) a 100 micron (149 mesh) filter used as a support material to prevent activated carbon fines from dropping into the upstream line (this filter should not to be confused with the two filters used to trap and measure activated carbon fines downstream of the column); (2) a layer of 1/4” support balls; (3) a layer of 1/8” support balls; (4) the activated carbon; (5) a layer of 1/8” support balls; and (6) a layer of 1/4" support balls (Table 3 and Figure 2).
Table 3: Column Loading Layer Mass (lbs./kg) Height (in/cm) 1/4-inch Support Balls 0.8/0.36 2.5/6.4 1/8-inch Support Balls 0.6/0.27 1.5/3.8 12x40 Activated Carbon 2.2/1.0 20/51 1/8-inch Support Balls 0.2/0.09 1.0/2.5 1/4-inch Support Balls 0.4/0.18 1.5/3.8
a) Layer of 1/8” Support Balls b) Activated carbon c) Layer of 1/4" Support Balls
Figure 2: Pilot Vessel Packing
2. Preparation of Contaminated LP Gas Supply The contaminants were pre-measured by weight into a clean beaker. The contaminants were added to the clean propane in proportions and levels similar to those in previously analyzed commercial LP Gas streams. The actual concentrations in the feedstock used for comparison with the results of the treated LP Gas were determined by a gas chromatographic based method (see Section V.E.: Results and Discussion). A clean 25-gallon (95-L) propane tank was partially filled with propellant-grade propane. The contaminants were then poured into a clean propane delivery hose and the hose was reconnected to the tank. The contaminants were flushed
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from the hose into the tank as it was filled (to ~80% full) with propellant grade propane. The 25-gallon tank was subsequently shaken and rolled to thoroughly mix the contaminants throughout the filled vessel.
3. Wetting Pre-process “wetting” of the activated carbon is required to remove air from the activated carbon pores7. The wetting procedure consisted of two steps: (1) carbon dioxide (CO2) pre-loading to minimize the amount of heat released during wetting with the process fluid, and (2) wetting with propellant-grade propane. The intent of CO2 preloading is to reduce the heat of adsorption when propane is introduced. The activated carbon first warms from the exothermic loading of CO2, then cools over time. CO2 was introduced into the activated carbon bed and pressurized to 14.7 psig (2.0 bar). The temperature of the bed initially increased as expected, and was allowed to stabilize over ~1.5 h. This procedure was recommended by the activated carbon manufacturer, but if it is found unnecessary in future tests, it should be eliminated to facilitate field implementation. Next, propellant grade propane was introduced. The propane flow is to be fast enough to allow the propane to act as a heat sink, (although the CO2 also acts to reduce heat as it desorbs). There was an initial heat rise of ~60 °F (15.6°C) as propane vapor flowed through the bed, followed by a rapid temperature drop as liquid filled the system (Figure 3). The vessel valves were then closed and the activated carbon bed with liquid propellant grade propane was left undisturbed for ~1 h.
40
60
80
100
120
140
0 50 100 150 200 250 300 350 400 450 500
Time (seconds)
Tem
pera
ture
(°F)
Inlet Temperature Outlet Temperature Figure 3: Column Temperature During Wetting Procedure
4. Decontamination and Sampling
After the wetting procedure, the contaminated supply tank was attached to the vessel containing the activated carbon bed, and flow of the contaminated LP Gas stream through the bed was initiated. Based on discussions with project advisors the process flow was directed upwards through the column against gravity. The
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flowrate was calculated by monitoring the drop in weight of the contaminated supply tank over time. Adjustments were made as needed to maintain a predetermined optimal flowrate. This desired flowrate was calculated based on project advisors’ recommendations and on prior exchanges with CEC. The process was scaled down based on cross-sectional area to maintain the same superficial velocity of LP Gas flow in the smaller pilot vessel. The flowrate is reported per cross-sectional area of the column to provide a means for comparison of flow between two different sized columns and to more easily indicate the contact time with the activated carbon through the length of the bed. The first sample was drawn after flowing through approximately one bed-volume of contaminated supply. Over the course of the first pilot test, nine (9) samples were drawn at regular time intervals (Figure 4). Two (2) additional samples - one of the contaminated supply and one of the propellant grade propane - were also taken. The temperature of the system was monitored, but not controlled throughout the course of the experiment. There were no significant temperature changes during the experiment. Ambient temperatures remained at ~70°F (21°C) until night time when the temperature dropped to ~62°F (17°C). Pressures were constant at 170 psig (12.7 bar).
0.00
5.00
10.00
15.00
20.00
25.00
0 2 4 6 8 10 12 14 16 18 20LP Gas Processed (gal)
Vol
umet
ric F
low
rate
(gal
/min
-ft²)
Sample #1
Sample #2
Sample #3
Sample #4
Sample #5
Sample #6
Sample #7
Figure 4: LP Gas Flowrates During First Test
5. Activated Carbon Fines
100 micron and 5 micron filters were weighed (dry) prior to their installation downstream of the activated carbon. These filters were later removed after the contaminated propane testing was completed, and re-weighed (dry).
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E. Results and Discussion 1. Contaminant Removal
The analytical method [prEN 15470:2006 (E)] was modified to use heptane as the internal standard because octane was one of the selected contaminants. Some samples were not analyzed. In-line (or on-site) analysis was also not possible. Sample #4 was selected for analysis because it had the lowest flowrate during sampling (closest to the predicted optimal flowrate and presumably with the greatest potential for contaminant removal). Sample #5 was selected for analysis because it had a higher flowrate during sampling and was taken shortly (1.3 gal / 4.9 L) after Sample #4 was completed. Sample #6 was selected for analysis as an intermediate flowrate sample taken shortly (1.3 gal / 4.9L) after Sample #5. The expected Contaminated Propane concentration (based on what was weighed and poured into the propane transfer hose) differs significantly from the concentration measured with the GC method (Table 4). Several possible factors could contribute to this discrepancy. One is that not all of the contaminant mixture was transferred from the weighed beaker to the transfer hose. The mixture was viscous and a visible amount was unavoidably left on the beaker wall. Given that the total contaminant volume added was 19.3 mL (0.65 oz), this loss of contaminant to the beaker may have been a significant error source. Another possible source of contaminant loss was inside the transfer hose. Some of the contaminant may have either been absorbed by the hose or adhered to it. A third factor may have been whether the contaminants, once introduced to the tank, were actually mixed homogenously throughout the propane (as intended). Some of the contaminants may have been adsorbed by the propane tank wall.
Table 4: Weight and GC Based Concentrations of Each Contaminant in First Test Concentration (mass ppm) Contaminants (order of
increasing boiling pt.) Expected (by weight) GC % Diff. n-Octane 119 19 84% Dioctyl adipate 95 27 72% Methyl linoleate 59 19 68% Pentadecane 119 42 65% Butyl benzyl phthalate 86 32 63% Total∗ 479 141 71%
Although the GC test method itself may have been a source of some loss, it is not likely that the heavy contaminants would have evaporated off to a large extent. The test method was modified to keep the evaporation temperature relatively low (25°C / 77°F) to avoid such losses. Although there is an apparent correlation between the boiling points of the contaminants used and the amount of loss of each contaminant, the contribution of evaporation to residue loss is undetermined. ∗ “Total” value varies slightly from the sum of the listed contaminants as it is an independent measurement of total residue.
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Based on these results, a new method to introduce contaminants with minimal loss was used in subsequent tests. Because the same GC method was used to measure both the Contaminated Supply and the processed samples, the above described concentration discrepancy was not considered a significant factor in the evaluation of the tested activated carbon’s ability to remove heavy-ends. It should also be noted that on-site immediate analysis of these samples during the course of the tests was not possible, and therefore the results could not be known until after all the tests were completed. The possibility of the Contaminated Supply concentration changing over time should be addressed the in future tests (See Section VI. F). The results from Samples #4, #5, and #6 clearly indicate effective removal of the contaminants selected for this initial protocol (Table 5). The results indicate that either lower flowrate results in better n-octane removal or that between Samples #4 and #5 the activated carbon became loaded to the point that it was unable to further adsorb n-octane. Another possibility is that other larger contaminants began to displace n-octane in the adsorption sites. The additional analysis of Sample #6 does not provide any additional support to the idea that a lower flowrate would result in better n-octane removal. However, the analyst indicated that there was some evidence of a small leak in the sample vessel. If this is the case, it is likely that the lighter molecules (i.e. propane) evaporated, leading to an erroneously high concentration of the contaminants (i.e. octane) left in the sample vessel. Whether n-octane could be further adsorbed by the activated carbon is uncertain at this point.
Table 5: Concentration of Contaminants in Samples from First Test Concentration (mass ppm)
Sample
LP Gas Processed (gal.)
Average Sample Flowrate (gal/min-ft²) Octane Pentadecane
Methyl linoleate
Dioctyl adipate
Butyl benzyl phthalate Total
Propellant-grade N/A N/A 0 0 0 0 0 1 Supply N/A N/A 19 42 19 27 32 141 #4 8.4 1.9 11 0 0 0 0 12 #5 11.7 10.7 21 0 0 0 0 22 #6 13.0 7.5 20 0 0 0 0 24
Adsorption capacity of the activated carbon for the added contaminants was not determined. However, a predicted adsorption capacity based on manufacturer estimates and from project advisors’ experience suggests that the volume of contaminated propane processed in this experiment was far less than what could be expected to be treated before the activated carbon pores are loaded. Breakthrough (the point at which the activated carbon no longer adequately removes selected contaminants) was determined in subsequent tests. This would provide an indication of how much contaminated LP Gas could be processed by a given amount of activated carbon (given that no channeling occurs in the adsorption bed).
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Removal of the lighter contaminant (octane) was not the primary focus of this test, but as octane is representative of some LP Gas contaminants, this test reveals that additional work beyond the scope of this project may prove beneficial if higher removal rates of such contaminants are desired. It can be concluded that full removal of the four other contaminants, over a processed volume of ~11.7 gal (44.3 L), could be achieved using this bed dimension and a flowrate of 10.7 gal/min-ft2 (436 L/min-m2). There was no measured distinction between the concentration of the contaminants in Samples #4, #5, and #6 (all are 0 ppm), so there is no indication of the effect of a change in flowrate (faster or slower than 10.7 gal/min-ft2) on contaminants removal.
2. Activated Carbon Fines Both the 5 micron and 100 micron polyester filters had visible activated carbon fines, and a measurable increase in weight after drying (Table 6). The filters, however, were not visibly clogged with activated carbon fines. Also, some of the additional mass can be attributed to metal pipe shavings and thread compound which were also clearly visible on the filters. It was not possible to separately measure to what extent this metal and thread compound contributed to the mass deposited on the filters. It was expected and later determined that the amount of metal and thread compound found on the filters significantly decreased in future tests with the same test vessel.
Table 6: Activated Carbon Particles Collected in First Test Filter Size Mass Collected (g / oz) 5 micron 0.10 / 0.0035 100 micron 0.17 / 0.0060
Figure 5: Filters (Post-Process) Showing Activated Carbon Fines and Other Debris
F. Proposed Next Steps The initial tests successfully demonstrated contaminant removal, and supported further experiments (See Section VI).
a) 100 micron (149 mesh) Filter
b) 5 micron (2500 mesh) Filter
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VI. Second Small Scale Propane Decontamination Test A. Summary
Based on the results and know-how gained from the first test, this second test was designed and conducted to determine the effect of activated carbon on odorized HD-5 LP Gas that contains actual LP Gas residues and compounds representative of heavier residues (C20+). The activated carbon bed was also shortened to be in proportion to the design of the proposed full-sized column and to better characterize the breakthrough of each contaminant. Also addressed were the reduction of the apparent loss of contaminants added to the supply tank; better flow control at a low flowrate; and eliminating metal debris as a source of error from the polyester filters.
B. Objectives (1) Determine the effect of a specific type of activated carbon on the
removal of selected concentrations of “heavy” contaminants from LP Gas processed at a pre-determined flowrate.
(2) Measure effluent activated carbon fines at a given process flowrate. (3) Measure process temperatures and pressures to better predict
process conditions in future experiments. (4) Achieve breakthrough of contaminants. (5) Use a lower length to diameter activated carbon bed ratio (scalable
to the full-sized DOT transportable full-sized vessel). (See Section VII)
(6) Determine the effect of the activated carbon adsorption process on mercaptan sulfur (i.e. odorant) concentration in the tested LP Gas.
C. Experimental Setup and Materials 1. Activated Carbon
The same type of activated carbon was used as in the first experiment.
2. Support balls 1/8” and 1/4” ceramic balls were used to support the activated carbon and to evenly distribute flow inside the vessel.
3. Filters New 100 micron x 0.100” (2.54 mm) thick and 5 micron x 0.080” (2.03 mm) thick polyester felt filter sheets were cut to fit the modified Impco VFF30 filter housings. The filters were used to determine the approximate size and amount of effluent activated carbon fines which are entrained at specific flow conditions.
4. Contaminants The following compounds were obtained and added to HD-5 LP Gas (Table 7):
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Table 7: Description of Contaminants Added for Second Test Contaminant Description n-Octane (C8H18) a representative compound of gasoline contamination Dioctyl adipate (C22H42O4) a plasticizer and known LP Gas contaminant American Welding & Tank residues (a blend of many contaminants from LP Gas tanks)
7% recovered at n-C8 boiling point; 54% recovered at n-C11 boiling point; 95% recovered at n-C20 boiling point (Determined by ASTM D2887)
Mobil Rarus 427 compressor oil ISO 100 (viscosity) with 100% recovered above n-C20 boiling point
The proportions added were weighted to ensure higher concentration of heavy (C20+) compounds. The actual concentrations in the feedstock used for comparison with the results of the treated LP Gas were determined by a gas chromatography based method. The American Welding & Tank residues were collected from used and recovered LP Gas tanks from throughout the eastern U.S. These residues are thought to be representative of contaminants found in commercial LP Gas streams, although not necessarily those found in fuel system residues. ASTM D2887 analysis was used to provide the above characterization. Additionally, the total sulfur concentration (using ASTM D 4294) was 6.56 mass %.
D. Procedure 1. Column Preparation
All valves to the column were vented, and the top cover and filter housings were removed. A flowmeter was installed downstream of the vessel. After removing support balls and activated carbon from the previous experiment, all exposed parts (e.g. filter housing interior, fittings with excess pipe compound) were first wiped clean with a cloth, and then the entire system was filled and flushed with pure propane. After flushing, the system was vented. Prior to loading the activated carbon vessel, the apparatus was placed on a scale. The activated carbon vessel was then loaded (from bottom up – the direction of process flow is up) with: (1) a 100 micron filter used as a support to prevent activated carbon fines from dropping into the upstream line, (2) a layer of 1/2” support balls, (3) a layer of 1/4” support balls, (4) a layer of 1/8” support balls, (5) the activated carbon, (6) a layer of 1/8” support balls, and (7) a layer of 1/4" support balls, and (8) a layer of 1/2” support balls (Table 8). The extra support balls were used as a means to shorten the activated carbon bed length within the same column used previously.
Table 8: Column Loading Layer Mass (lbs./kg) Height (in/cm) 1/2-inch Support Balls 0.8 / 0.36 3.5 / 8.9 1/4-inch Support Balls 1.4 / 0.64 4 / 10 1/8-inch Support Balls 1.0 / 0.45 2.5 / 6.4 12x40 Activated Carbon 0.6 / 0.27 7 / 18 1/8-inch Support Balls 1.0 / 0.45 3.1 / 7.9 1/4-inch Support Balls 1.0 / 0.45 3.5 / 8.9 1/2-inch Support Balls 0.8 / 0.36 2.9 / 7.4
2. Wetting
As before, a wetting procedure was conducted (CO2 pre-loading followed by wetting of the activated carbon with propellant-grade propane). After flowing
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CO2, through the column, the outlet valve was closed and the system was pressurized to 14.7 psig (2.0 bar). There was no measurable temperature change. The system was then kept under pressure for ~1.5 hours. Propellant-grade propane was then introduced, but unlike the first test, there was no measurable temperature rise. This likely occurred because the bed in this test was smaller, which would result in less heat released, and also less time to fill with liquid phase LP Gas. Additionally, because of the smaller bed size, the temperature probes were further away from the activated carbon. Because there was no temperature differential, the outlet and inlet valves were closed once it was determined that liquid had entirely filled the column. The wetted system was left closed overnight.
3. Preparation of Contaminated LP Gas Supply The contaminants were pre-measured by weight into a clean glass beaker. A clean 100-gallon (379 L) propane tank was then partially filled (~20%) with HD-5 LP Gas. A short metal pipe with a fitting for the LP Gas delivery hose was attached to the tank inlet valve. The contaminants were then poured into the pipe and flushed into the tank as it was filled (to ~85% full) with HD-5. The beaker used to pour the contaminants was re-weighed to account for contaminant loss. The 100-gallon “contaminated supply” tank was then shaken and rolled to thoroughly mix the contaminants throughout the filled vessel. The tank was left undisturbed overnight. The next morning, the contaminated supply tank was again rolled and shaken. A nitrogen supply line was then connected to the vapor valve of the supply tank, and a pressure head of ~185 psig (13.8 bar) was applied to the contaminated supply.
4. Decontamination and Sampling Following the wetting procedure, the contaminated supply tank was attached to the activated carbon vessel, and flow of the contaminated LP Gas stream through the bed was initiated. Adjustments were made, if necessary, to maintain a predetermined optimal flowrate. The flowmeter installed for this test did not function properly; so it did not improve flow monitoring and control vs. the first experiment. Flow was measured by monitoring the increase in weight of the receiving vessel over time. Flow adjustments were made manually by decreasing the vapor pressure in the receiving vessel and/or opening the vessel outlet valve. This receiving vessel was not used for sample collection. Each aluminum sample vessel was first cleaned with propellant grade propane, vented, and then filled with nitrogen to ~80 psig (6.5 bar) as a means to control the pressure differential created when the LP Gas sample line is first connected to for filling. Aluminum vessels were used at the recommendation of project advisors. The flowrate was controlled in the same way as in the first test. The first sample was drawn after flowing through approximately one bed-volume of contaminated supply. Over the course of the pilot test, seven (7) samples were drawn at regular time intervals. An eighth sample was being collected as the contaminated LP Gas supply ran out. A sample of both the contaminated supply, and the HD-5 spec LP Gas were also taken.
17
5. Activated Carbon Fines
100 micron and 5 micron filters were weighed (dry) prior to their installation downstream of the activated carbon. These filters were later removed after the contaminated LP Gas propane testing was completed, and re-weighed (dry).
E. Results and Discussion 1. Contaminant Removal
A modified prEN 15470:2006 (E) method was again used for sample analysis, with heptane as the internal standard and a lower evaporation temperature (25°C).
Table 9: Weight and GC Based Concentrations of Each Contaminant in Second Test Concentration (mass ppm) Contaminants Expected (by weight) GC Determined % Difference
n-Octane 53 15 72% Dioctyl adipate 57 28 51% American Welding & Tank Residues 211 98 54% Mobil Rarus 427 Compressor Oil 346 196 43% Total 667 337 50%
The expected contaminated LP Gas concentration (based on what was weighed and poured into the tank) again differed significantly from the concentration determined with gas chromatography (Table 9). This difference is a concern that should be addressed as test methods for this purpose are further developed. There was, however, a significant improvement in the efficiency of addition of the contaminants from the previous test. In this test, the amount of residual contaminants remaining on the beaker walls was accounted for by weight, but this resulted in only a slight reduction (0.6%) in the expected concentration. Although the shorter, steel transfer pipe likely led to better transfer of the contaminants to the tank, some of the contaminant may have still adhered to the pipe surface or, once introduced to the tank, settled or been adsorbed onto the tank walls instead of dispersing homogenously throughout the LP Gas. One possible improvement to in future work is to pre-dissolve the contaminants in a lighter solvent such as pentane or toluene prior to addition to the LP Gas. Results show that for this flowrate and bed dimensions the activated carbon removed significant amounts of all the added contaminants. The amount of contaminant removed and the time to breakthrough varied for each contaminant (Figures 6 & 7 and Table 10). As LP Gas is processed, contaminants with lesser affinity for activated carbon may be displaced by compounds that are more readily absorbed. The process was effective in removing the compressor oil and dioctyl adipate (which contained the majority (~98%) of C20+ compounds used in this test). The concentration of these contaminants remained at below 10% of their initial concentrations (>90% removal) and below a combined 15 ppm until after 241 bed volumes (47 gal.) of LP Gas were processed. This achieves the goal initially set for these tests of reaching less than 25 ppm C20+ heavy-ends content in the decontaminated product.
18
Table 10: Concentrations of Heavy-Ends Contaminants and Ethyl Mercaptan (Ethanethiol) for Second Test
LP Gas Processed Sample Flowrates
(gal/min-ft²) Concentration (mass ppm) Sample No.
Bed Volumes Gallons Average Max Octane
Dioctyl Adipate
AW&T Residue
Compressor Oil
Total Residues Ethanethiol
Supply N/A N/A N/A N/A 15 28 98 196 338 14.3 1 11 2 1.8 9.6 2 0 7 7 17 2 2 62 12 1.5 7.5 2 0 12 7 21 8.9 3 119 23 2.0 6.4 4 0 35 7 46 11.9 4 177 34 2.7 5.3 11 1 59 13 85 5 241 47 2.0 4.3 5 2 47 11 65 6 297 58 2.2 4.3 14 16 91 32 153 7 332 65 1.9 5.3 11 25 86 35 157
Because contaminated LP Gas flow during sampling varied more than anticipated, for each sample are listed both the average flowrates during sampling and the maximum flowrate which occurred as the sample was being taken (Table 10). Both these flowrates are relevant as a high average flowrate may not allow enough contact time with the activated carbon to achieve maximum contaminant removal, or alternatively one or more flowrate “spikes” during a 2-gal (7.6 L) sample may significantly impact the concentration taken for the whole sample. This is a likely reason that the concentrations of most contaminants in Sample #4, which had the highest average flowrate, were higher than those found in Sample #5.
Table 11: Concentration of Sulfur Compounds for Second Test LP Gas Processed Concentration (mass ppm as S) Sample No.
Bed Volumes Gallons Ethanethiol
1-Butanethiol
Diethyl Sulfide
Diethyl Disulfide
1-Heptanethiol
1-Octanethiol
Isopropyl Disulfide Total
Supply N/A N/A 7.4 0.2 3.6 8.8 0.7 1.2 0.2 22.1 1 11 2 1.0 0.2 3.1 9.0 13.3 2 62 12 4.6 0.3 3.2 6.3 0.5 1.1 16.0 3 119 23 6.1 0.2 3.2 8.5 0.5 1.0 19.5
Analysis of sulfur compounds in the LP Gas suggests that they are less readily removed by the selected activated carbon than the heavy-ends residues (Table 11). Of particular note, ethyl mercaptan (ethanethiol) is initially reduced to 14% of its original level (Sample #1), then returns to 62% (Sample #2) within 62 bed volumes, and 82% within 119 bed volumes (Sample #3). This suggests that heavy-ends removal can continue long after the ethyl mercaptan is no longer removed by the activated carbon.
19
0
2
4
6
8
10
12
0 10 20 30 40 50 60 70 80
LP Gas Volume Processed (gal)
Aver
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/min
-ft²)
0.00
0.10
0.20
0.30
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0.70
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0.90
1.00
Nor
mal
ized
Con
tam
inan
t Con
cent
ratio
n
Octane Dioctyl Adipate AW&T Residue Compressor Oil Total Residues Ethanethiol
Figure 6: Flowrate Overlaid by Breakthrough Curves (Normalized) for Second Test
0
2
4
6
8
10
12
0 10 20 30 40 50 60 70 80
LP Gas Volume Processed (gal)
Aver
age
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ectio
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(gal
/min
-ft²)
0
20
40
60
80
100
120
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160
180
Con
tam
inan
t Con
cent
ratio
n (p
pm)
Octane Dioctyl Adipate AW&T Residue Compressor Oil Total Residues Ethanethiol Figure 7: Flowrate Overlaid by Breakthrough Curves (Concentration) for Second Test
20
2. Activated Carbon Fines Both the 5 micron and 100 micron polyester filters had visible activated carbon fines, and a measurable increase in weight, but no evidence of metal particles or other debris. There was no measurable pressure drop at any point in the test that would indicate that the process was affected by these fines.
Table 12: Activated Carbon Particles Collected in Second Test Filter Size Mass Collected (g / oz) 100 micron 0.03 / 0.001 5 micron 0.05 / 0.002
F. Proposed Next Steps
The second tests demonstrate effective removal of heavy-end contaminants from LP Gas. Suggested next steps based on these results are:
(1) Pilot scale tests using a higher flowrate (desirable for larger commercial applications);
(2) Pilot scale tests with a lower total heavy-ends concentration (~200 ppm) and lower C20+ heavy-ends concentration (~100 ppm)
(3) Full-scale tests with LP Gas contamination levels as in #2 above. As flow control continued to be problematic in the second tests, a crucial piece of subsequent work will be a better flow control system. Future tests should also determine if the concentration in the Contaminated Supply changes over time.
VII. Full Scale Column & Process Design A full sized column was designed and manufactured (Figures 8 & 9) to help with future steps in follow-on tests. The vessel was designed to be DOT approved transportable, while providing adequate LP Gas flow design, and was subject to the constraints of Table 13. DOT approval allows for the option to switch out the entire column when the activated carbon no longer effectively removes contaminants (rather than regenerating or replacing the activated carbon). (See Sections IX.A and X).
Figure 8: Full Sized Column Design
21
Table 13: Full Sized Column Design Constraints
Footprint 48”x48” (1.2 m x 1.2 m) Weight <3,200 lbs. (1,450 kg) when full (able to be lifted with standard equipment) Length ~72” (able to fit inside a standard freight truck) Pressure rated to 250psi at 650°F (to allow for the option of future work with high
temperature in-situ activated carbon regeneration)
The design also includes interior screens and a diffuser plate at the inlet designed to disperse the LP Gas evenly throughout the adsorption medium as well as to incorporate inert support balls for the adsorbent.
Figure 9: Process Flow Diagram
After CEC engineers calculated expected flow rates and made recommendations on the tank re-design dimensions based on their prior work, the initial vessel design was further refined with a reduced outer diameter (24” / 61 cm). This smaller diameter design reduces manufacturing cost and is likely to reduce undesirable channeling of the LP Gas through the activated carbon bed. The desired flow rate for the reduced diameter vessel was accordingly lowered. The length to diameter ratio in this large scale vessel was modeled in the pilot experiments, and the flowrates tested in the pilot tests were scaled to maintain the same cross-sectional flowrate as in the full-scale column (Table 14). The pilot unit to full-scale flowrate ratio is 1:67 (1:560 by volume), which is well within the 1:1000 max ratio commonly used and accepted for process scalability.
22
Table 14: Comparison of Full Scale and Pilot Columns Dimensions Full-Sized Column Pilot Scale Column Bed Length (in) 56.4 6.8 Bed Diameter (in) 23.6 2.87 Length to Diameter Ratio 4.8 4.9 Cross-sectional Area (ft2) 3.0 .045 Volumetric Flowrate (gal/min) 6.0 .09 Cross-sectional Flowrate (gal/min-ft2) 2.0 2.0
VIII. Economic Analysis Last fall, the additional cost paid in Southern California for premium LP Gas with low heavy-ends content was ~$0.10/gallon at $2.10 to $2.25 retail pricing. For a decontamination process to be economically viable, the total cost must be sufficiently below this $0.10/gal premium to achieve payback over a reasonable period. The above described full-sized column was used for the below economic analysis (Table 15, see Appendix 3 for full analysis). Additionally, the following assumptions were made:
(1) Total heavy-end contaminants in the supply stream are 338 ppm, including ~229 ppm of C20+ based on boiling point analysis of the contaminants in second test (see Table 10 and Appendix 2). Lower concentrations of these contaminants in the LP Gas will likely result in a greater volume of treated LP Gas prior to breakthrough, and thus a lower cost per volume of clean product.
(2) Replacement of activated carbon is required after the C20+ residues content exceeds 25 ppm. In the experiments used for this analysis, the last measured sample with C20+ content below 25 ppm was at 13 ppm (or <10% of the initial concentration) at which point 241 bed volumes had been processed. The total residues concentration at this measurement was 65 ppm (or <20% of the initial concentration). For this reason, 241 bed volumes was used as the capacity of the activated carbon before replacement.
(3) The process flowrate is 6 gal/min. (4) For this analysis, the per-gallon revenue to be generated by the full
scale plant is taken to be the known additional cost recently paid for low-residue LP Gas ($0.10/gal)
Table 15: Economic Analysis Summary
Annual Production (gal) 1,057,536 Fixed Capital $ 89,874 Working Capital $ 8,987 Total Capital Cost $ 98,862 Annual Manufacturing Cost $ 64,948 Annual Revenues $ 105,754 Project Life (years) 15 Tax Life (years) 15 Payout time (years) 2.74
23
The total cost per gallon of clean product is $0.061. This analysis yields a payout time of 2.74 years. IX. Field Service Recommendations Pending full scale implementation and testing of this activated carbon LP Gas decontamination process, the following recommendations can be made based on initial tests:
A. Pre-process Wetting and CO2 Pre-loading The activated carbon must first be properly wetted to achieve optimal results. This is an essential step in the process. One option envisioned for field implementation is that “module” columns are pre-packed and can be switched out when breakthrough is reached (when the activated carbon must be replaced). In this case, the carbon dioxide preloading step can be performed at the column packing site. If future tests determine that CO2 pre-loading is not necessary, this step can be eliminated. Wetting is conducted by flowing LP Gas through the column until it is filled with liquid and the temperature differential between inlet and outlet streams is less than 10°F (5.5°C) (if necessary, the LP Gas used for this procedure can be recycled back through the column). At this point, the vessel valves should be closed and the LP Gas is left undisturbed for at least one hour7.
B. Flowrate The flowrate used to process the contaminated LP Gas is critical to achieve optimal contaminant removal. It is expected that an increased flowrate will result in lower removal of contaminants. (Note: The precise effects of such changes must be tested to better understand the effects of this key variable). Care must be exercised so that upon start-up, the flow of propane is not started abruptly in a manner which may lead to disruption of the packed bed and possible loss of activated carbon or formation of “channels”.
C. Breakthrough and Activated Carbon Replacement The quality of LP Gas upstream and downstream of the column must be monitored regularly. The concentration of various contaminants in the supply stream will affect the amount to which the activated carbon can remove contaminants, and how much product may be treated before the activated carbon must be replaced. Based on the above results, it can also be anticipated that an increase in the effluent concentration of lighter residue components will likely precede breakthrough of the heavier heavy-end residues. The above heavy-ends removal capacity of the activated carbon is provided as an estimate based on pilot tests conducted to date at specific conditions.
D. Filters Initial experiments show that some fine activated carbon particles are entrained in the product stream and can be captured by filters downstream of the column. In tests, these particles were not sufficient to impact the flow of product by
24
clogging the filters; however, the pressure difference across these filters should be monitored to determine if filters need to be replaced.
E. Ethyl Mercaptan Caution Because ethyl mercaptan content is initially reduced, caution should be exercised. LP Gas downstream of the activated carbon column during this initial period of operation may not be sufficiently odorized to indicate a potential leak. X. Operating Options Two possible options for the replacement of spent activated carbon decontamination process are:
(1) Spent activated carbon from LP Gas dealers is regenerated at a propellant manufacturer who already has equipment necessary for regeneration on-site. This propellant manufacturer would supply the LP Gas dealer with regenerated activated carbon.
(2) Spent activated carbon would be collected, regenerated, and replaced by the activated carbon manufacturer.
Refinery
LP Gas Dealer LP Gas Dealer
Propellant Manufacturer
LP Gas Clean-up Site
LP Gas Clean-up Site
Spent Medium (catalyst impregnated AC) Regeneration Site
Option 1: Regeneration of Spent AC at Propellant Manufacturer’s Site
Refinery
LP Gas Dealer LP Gas Dealer
AC ProviderLP Gas
Clean-up Site
LP Gas Clean-up Site
Option 2: Spent AC Regenerated or Disposed of by AC Provider
Figure 10: Activated Carbon Regeneration Schemes XI. Conclusions These activated carbon tests have demonstrated that certain heavy-end contaminants can be significantly removed from LP Gas. The latest tests show the process to be particularly effective in removing heavier contaminants (i.e. C20+ heavy-ends). Additionally, the results show that ethyl mercaptan concentration is reduced by the process, but reappears in the product stream more quickly relative to other
25
contaminants – suggesting that heavy-ends may continue to be removed while mercaptans are not. However, addition of more ethyl mercaptan may be required to ensure that the final product has a suitable (and legally defensible) concentration of odorant. Initial economic analysis suggests that this process can be viable. Further development is recommended. XII. Future work As stated above, proposed immediate next steps based on the results of the latest tests are:
(1) Pilot scale tests using a higher flowrate (desirable for larger commercial applications);
(2) Pilot scale tests with a lower total heavy-ends concentration (~200 ppm) and lower C20+ heavy-ends concentration (~100 ppm)
(3) Full-scale tests with LP Gas contamination levels as in #2 above. Additionally, future work may include a comparison of analytical methods (i.e. CEN and CEC) or variations on these methods. ASCENT has also discussed the possible implementation of a novel method to achieve reasonably priced in-situ regeneration. This aspect of the decontamination process may be developed as an eventual follow-up if the disposal option of the spent activated carbon by the activated carbon provider turns out not to be viable. XIII. Acknowledgements ASCENT is grateful to PERC for support and funding of this project. For their ongoing assistance, we thank our advisors: John Ehlers, Bob Falkiner, George Maes, John O’Connor, Andy Pickard, Arnie Smith, Jean-Paul Trespaille, and Quan Zhuang. For their invaluable help ASCENT is also indebted to Ernie Reed (Aeropres Corporation); Larry Osgood (Consulting Solutions), Mical Renz (Dixie Services, Inc.); Junichi Yodotani and T. Kioyosawa (Cosmo Engineering Co.); Jerry Gilliam and Walker Ogden (American Welding and Tank); Steve Moore (Expo Propane), Dan McCartney (Black & Veatch), and Bob Myers (PERC).
1 J. O’Connor, Phillips Petroleum Company, “Process for Removing Oil from Liquefied Petroleum
Gas,” U.S. Patent 5,474,671, (Filed April 11, 1994, Issued December, 12, 1995)
26
2 T. Hideo et. al., Cosmo Engineering Co. Ltd., “Method of Removing Residue in Liquefied Gas
and Regenerating Method of Activated Carbon,” Japan Patent 2001-294415, (Filed April 13, 2000)
3 ASTM D 2158, “Standard Test Method for Residues in Liquefied Petroleum (LP Gases),” (West Conshohocken, PA: ASTM International, 2002)
4 Q. Zhuang and A. Pickard, CANMET Energy Technology Center, “Accurate Measurement Method for Residues in LPG” (presented to CGSB Committee on Petroleum Test Methods, November 18, 2004)
5 Q. Zhuang, J. Yodotani, and M. Kato, “Accurate measurement method for the residues in liquefied petroleum gas (LPG),” Fuel Vol. 84 (2005): 443-446
6 M. Mamakos, J.Meyer, A. Spataru, “Discussion of LP Gas Fuel and Residues Collected from Microturbine Powered Hybrid Electric Vehicle Sites,” (The ADEPT Group, Inc, March 2005)
7 S. Carr, “CO2 Pre Loading Followed by Organic Wetting,” (Pittsburgh, PA: Calgon Carbon Corporation, 1999)
Appendix 1
28
First Test Log
Time (min)
Comment T1 (°F)
T2 (°F)
P1 (psi)
P2 (psi)
P3 (psi)
P4 (psi)
0:00 Begin test 150 160 1:30 170 170 170 170 5:30 Sample 1 7:30 Receiving tank outage gauge opened
briefly
13:00 Testing stopped briefly 14:00 Sample 2 170 170 170 170 16:25 68 68 20:00 27:30 Sample 3 36:30 70 68 175 170 170 170 44:00 Begin Sample 4 67:45 End Sample 4 70:15 Testing stopped briefly 73:30 Sample 5 80:45 Sample 6 94:30 Nighttime – ambient air cooler 62 62 175 175 170 170 96:00 Testing stopped briefly 99:30 Sample 7
110:45 Testing ended Samples 8&9
Temperature and pressures remained steady between times noted. T1: Temperature at column inlet T2: Temperature at column outlet P1: Pressure at column inlet P2: Pressure at column outlet P3: Pressure after 100 micron filter P4: Pressure after 5 micron filter
Sample ID Volume Processed Prior to Sample (gal.)
Average Flowrate During Sampling (gal/min)
Propellant-grade Propane N/A N/A Contaminated Propane 0.0 N/A
#1 1.76 0.76 #2 3.86 0.38 #3 6.10 0.38 #4 8.38 0.08 #5 11.71 0.57 #6 13.00 0.38 #7 15.57 0.57 #8 Receiving Tank N/A N/A #9 Receiving Tank N/A N/A
Appendix 2
Certificates of Analysis Dixie Services, Inc.
Galena Park, TX
30
CERTIFICATE OF ANALYSIS Number: 122255 Client: The ADEPT Group, Inc. Date: January 6, 2006
10866 Wilshire Boulevard, Suite 350 Los Angeles, CA 90024 Attention: Alex Spataru Sample: Three samples of propane, submitted 27 Dec 05
Marks: Pure C3H8; Test #1 Baseline; Test 1, #4
The subject samples were analyzed by test method CEN/TC19 N 1221 – Annex E, “Liquefied petroleum gases – Determination of dissolved residues – Gas chromatographic method,” except that the maximum evaporation temperature was limited to 25 °C and n-heptane was substituted for n-octane as the internal standard for the gas chromatographic analysis. The results were as follows:
Pure C3H8
Test #1 Baseline
Test 1 #4
Total residue, mg/kg 1 141 12 n-Octane, mg/kg 0 19 11 Pentadecane, mg/kg 0 42 0 Methyl linoleate, mg/kg 0 19 0 Butyl benzyl phthalate, mg/kg 0 32 0 Dioctyl adipate, mg/kg 0 27 0
Dixie Services Incorporated, Mical C. Renz MCR/s
31
CERTIFICATE OF ANALYSIS Number: 122255 Supplement Client: The ADEPT Group, Inc. Date: January 14, 2006
10866 Wilshire Boulevard, Suite 350 Los Angeles, CA 90024 Attention: Alex Spataru Sample: Propane, submitted 27 Dec 05
Marks: Test 1, #5 Fast
The subject sample was analyzed by test method CEN/TC19 N 1221 – Annex E, “Liquefied petroleum gases – Determination of dissolved residues – Gas chromatographic method,” except that the maximum evaporation temperature was limited to 25 °C and n-heptane was substituted for n-octane as the internal standard for the gas chromatographic analysis. The results were as follows:
Test 1 #5 Fast
Total residue, mg/kg 22 n-Octane, mg/kg 21 Pentadecane, mg/kg 0 Methyl linoleate, mg/kg 0 Butyl benzyl phthalate, mg/kg 0 Dioctyl adipate, mg/kg 0
Dixie Services Incorporated, Mical C. Renz MCR/s
32
CERTIFICATE OF ANALYSIS Number: 122255 Supplement 2 Client: The ADEPT Group, Inc. Date: February 1, 2006
10866 Wilshire Boulevard, Suite 350 Los Angeles, CA 90024 Attention: Alex Spataru Sample: Propane, submitted 27 Dec 05
Marks: Test 1, #6, 48455
The subject sample was analyzed by test method CEN/TC19 N 1221 – Annex E, “Liquefied petroleum gases – Determination of dissolved residues – Gas chromatographic method,” except that the maximum evaporation temperature was limited to 25 °C and n-heptane was substituted for n-octane as the internal standard for the gas chromatographic analysis. The results were as follows:
Test 1 #6
Total residue, mg/kg 24 n-Octane, mg/kg 20 Pentadecane, mg/kg 0 Methyl linoleate, mg/kg 0 Butyl benzyl phthalate, mg/kg 0 Dioctyl adipate, mg/kg 0
Notes
The sample cylinder was exhausted in the conduct of the test, and the total amount of sample available from the cylinder was less than from the previous test of Cylinder #5. The analyst observed that an LPG-like odor was detected before the test was started. Thus it seems likely that this cylinder had a very small leak Dixie Services Incorporated, Mical C. Renz MCR/s
33
CERTIFICATE OF ANALYSIS Number: 123314 Client: The ADEPT Group, Inc. Date: May 20, 2006
10866 Wilshire Boulevard, Suite 350 Los Angeles, CA 90024 Attention: Alex Spataru Sample: Eight samples of propane, submitted 19 Apr 06
Marks: Listed in tables below Date: 3/30/2006
Seven of the subject samples were analyzed for residue by test method CEN/TC19 N 1221 – Annex E, “Liquefied petroleum gases – Determination of dissolved residues – Gas chromatographic method,” except that the maximum evaporation temperature was limited to 25 °C and n-heptane was substituted for n-octane as the internal standard for the gas chromatographic analysis. Four of the samples were tested for sulfur compounds by ASTM D 5623, “Sulfur Compounds in Light Petroleum Liquids by Gas Chromatography and Sulfur Selective Detection. The results were as follows:
Contaminated Supply
Sample #1
Sample #2
Sample #3
Total residue, mg/kg 338 17 - 46 Sulfur compounds, mg/kg as S Ethanethiol 7.4 1.0 4.6 6.1 Ethanethiol, as C2H5SH 14.3 2.0 8.9 11.9 1-Butanethiol 0.2 0.2 0.3 0.2 Diethyl sulfide 3.6 3.1 3.2 3.2 Diethyl disulfide 8.8 9.0 6.3 8.5 1-Heptanethiol 0.7 - 0.5 0.5 1-Octanethiol 1.2 - 1.1 1.0 Isopropyl disulfide 0.2 - - -
Sample #4
Sample #5
Sample #6
Sample #7
Total residue, mg/kg 85 65 152 157 Dixie Services Incorporated, Mical C. Renz MCR/s
34
CERTIFICATE OF ANALYSIS Number: 123314 Supplement Client: The ADEPT Group, Inc. Date: May 22, 2006
10866 Wilshire Boulevard, Suite 350 Los Angeles, CA 90024 Attention: Alex Spataru Sample: Eight samples of propane, submitted 19 Apr 06
Marks: Listed in tables below Date: 3/30/2006
As requested, additional integration intervals have been applied to the chromatograms from the Total Residue test (method CEN/TC19 N 1221 – Annex E) to obtain estimates of the four components used to prepare the synthetic residue. The results were as follows (sum of individual components may not equal the total column because of rounding):
n-Octane
Dioctyl Adipate
LPG Residue
Oil
Total
Contaminated Supply (mg/kg) 15 28 98 196 338 Sample #1 2 <1 7 7 17 Sample #3 4 <1 35 7 46 Sample #4 11 1 59 13 85 Sample #5 5 2 47 11 65 Sample #6 14 16 91 32 153 Sample #7 11 25 86 35 157 Dixie Services Incorporated, Mical C. Renz MCR/s
35
CERTIFICATE OF ANALYSIS Number: 123314 Supplement 2 Client: The ADEPT Group, Inc. Date: June 20, 2006
10866 Wilshire Boulevard, Suite 350 Los Angeles, CA 90024 Attention: Alex Spataru Sample: Propane Sample #2, submitted 19 Apr 06
Marks: Sample #2 Date: 3/30/2006
As requested, Sample #2, which was previously tested for sulfur compounds, has also been analyzed for total residue (method CEN/TC19 N 1221 – Annex E). Estimates of the concentration of the four components used to prepare the synthetic residue were also obtained. The results were as follows:
n-Octane
Dioctyl Adipate
LPG Residue
Oil
Total
Sample #2, mg/kg 2 <1 12 7 21 Dixie Services Incorporated, Mical C. Renz MCR/s
36
CERTIFICATE OF ANALYSIS Number: 123914 Client: The Adept Group, Inc. Date: June 20, 2006
10866 Wilshire Boulevard, Suite 350 Los Angeles, California 90024
Attention: Nolan Sambrano Sample: Mobil Rarus 427 air compressor oil, submitted 7 Jun 06 Marks: Grainger # 4Zf21 D 2887 Boiling range, °C, % Recovery IBP 337.0 n-C20 = 344 1 355.5 n-C21 = 356 26 462.0 2 372.0 n-C22 = 369 27 463.5 3 383.0 n-C23 = 380 28 465.5 4 391.5 n-C24 = 391 29 467.5 n-C32 = 468 5 398.0 30 469.0 6 404.0 n-C25 = 402 31 470.5 7 409.0 32 472.5 8 413.5 n-C26 = 412 33 474.0 n-C33 = 479 9 417.5 34 475.5 10 421.5 n-C27 = 422 35 477.0 11 425.0 36 478.5 12 428.0 37 480.0 13 431.0 n-C20 = 431 38 481.5 n-C34 = 481 14 434.0 39 483.0 15 437.0 40 484.5 16 439.5 n-C29 = 440 41 485.5 17 442.0 42 487.0 18 444.5 43 488.5 19 447.0 44 489.5 n-C35 = 489 20 449.5 n-C30 = 449 45 491.0 21 451.5 46 492.0 22 453.5 47 493.5 23 456.0 48 495.0 24 458.0 n-C31 = 458 49 496.0 n-C36 = 496 25 460.0 50 497.0
37
Boiling Range, °C, % Recovery, continued 51 498.5 76 532.0 52 499.5 77 533.5 n-C42 = 534 53 501.0 78 535.0 54 502.0 79 536.5 55 503.5 n-C37 = 503 80 538.5 56 504.5 81 540.0 n-C43 = 540 57 506.0 82 542.0 58 507.0 83 543.5 59 508.5 n-C38 = 509 84 545.5 n-C44 = 545 60 509.5 85 547.5 61 511.0 86 549.5 62 512.0 87 551.5 63 513.5 88 553.5 64 515.0 89 556.0 65 516.5 n-C39 = 516 90 558.5 66 517.5 91 561.0 67 519.0 92 564.0 68 520.5 93 567.0 69 522.0 n-C40 = 522 94 570.5 70 523.0 95 574.0 n-C50 = 575 71 524.5 96 578.5 72 526.0 97 583.5 73 527.5 n-C41 = 528 98 589.5 74 529.0 99 599.0 75 530.5 FBP 606.0 n-C60 = 615 (n-Cnn = xxx entries above denote the boiling points of normal paraffins as reported in D 2887) Dixie Services Incorporated, Mical C. Renz MCR/s
Appendix 3
Economic Analysis
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Annual Production Capacity Process Flowrate 6 gal/min Daily Production Hours 10 hr Annual Production Days 306 days Operating Capacity 96% Daily Production 3456 gal
Total Annual Production 1,057,536 gal Activated Carbon Total Column Volume (gal) 130 gal Bed Volume (gal) 107 gal Bed Volume (cu ft) 14.3 ft^3 Activated Carbon Density 29 lb/ft^3 Filled Bed Weight 414.7 lb Lifetime before Replacement 241 bed volumes Lifetime before Replacement 25787 gal Usage Rate per Gallon Product 0.016 lb/gal produced Activated Carbon Cost 1.88 $/lb Filter Cartridges Unit Cost $ 18.00 $ Rate per Gallon Product 0.0001 units/gal Carbon Dioxide Cost $ 1.25 $/ft^3 Volume Per Pre-load 27.81 ft^3 Rate per Gallon Product 0.0011 ft^3/gal produced Product Quality Analysis Test Cost $ 150.00 $ Frequency of Test 0.0001 tests/gal produced Rent & Utilities Pump Size (hp) 3 hp Pump Size (kW) 2.2 kW Annual Power Consumption 6732 kW-hr Electricity Rate 0.081 $/kW-hr Annual Electricity Cost $ 545.29 $ Monthly Rent $ 60.00 $ Annual Rent $ 720.00 $ Labor Daily 0.5 hr Annual 153 hr Supervision & Payroll (20% of Labor) 30.6 hr Labor Rate 24 $/hr Annual Total $ 4,406.40 $ Capital Costs
Fixed Capital Quantity Unit Base Cost Module Factor-1 Cost (Installed)
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Activated Carbon Column 1 column $ 4,060.00 3.2 $ 12,992.00
Pump 1 pump $ 2,500.00 2.4 $ 6,000.00 Storage Tank (Horizontal) 1 tank $25,000.00 2.2 $ 55,000.00 Filter Housing 2 housing $ 560.00 1.2 $ 1,344.00 Support Balls 3.1 cu ft $ 45.00 1 $ 138.36 Gas Chromatograph 1 GC $12,000.00 1.2 $ 14,400.00
Subtotal $ 89,874.36 Working Capital (10% of Fixed) Subtotal 10.00% $ 8,987.44 Total Capital Cost $ 98,861.80 Manufacturing Cost Consumables Cost/gal Product Rate Annual Cost Activated Carbon $ 0.0302 $ 31,973.21 Filter Cartriges $ 0.0014 $ 1,476.38 Carbon Dioxide $ 0.0013 $ 1,425.40 Utilities $ 0.0005 $ 545.29 Rent $ 0.0007 $ 720.00 Labor $ 0.0042 $ 4,406.40 Analysis $ 0.0150 $ 15,863.04 Maintenance 5.00% of Fixed Capital $ 4,493.72 Supplies 1.50% of Fixed Capital $ 1,348.12 Taxes, Insurance 3.00% of Fixed Capital $ 2,696.23 Total Manufacturing Cost $ 0.061 $ 64,947.78
Price/gallon Annual Revenue
Revenues $ 0.10 $ 105,753.60 NPV Calculation Required Rate of Return 0.1 Salvage Value $ 19,500.00 $ Project Life 15 years Tax Life 15 years Tax Rate 0.5 Straight Line Depreciation $ 4,691.62 $/year NPV $ 80,986.47 Annualized NPV $ 10,647.60 Rate of Return at NPV=0 22% Payout time 2.74 years
Yearly revenues, expenses, and depreciation are taken to be constant so NPV is calculated based on the following expression: NPV = -(CI+Cw) + (R-X)(1-t)[1-(1+i)-n/i + Dt[1-(1+i)-n
t]/i +(Cs+Cw)/(1+i)n
Where: R = Annual revenues n = Project life (years) X= total Expenses nt = Tax life CI= Fixed capital investment i = Required rate of return Cs = Salvage Value t = Tax rate Cw = Working capital
Appendix 4
Test Methods
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Determination of Part Per Million Trace Components. Purpose: To analyze for part per million levels of contaminants in feedstock.
Such as unsaturated compounds, and hexane+ hydrocarbons.
All Incoming and outgoing product is required to have the trace contaminate analysis performed. The product must meet the predetermined specification of either the customer or Aeropres.
A 300cc stainless steel sample container equipped with toggle valves on each end is to be used for sample procurement. The cylinder is attached to the vessel to be sampled via a rubber hose. The sample cylinder is to be purged a minimum of three times. Fill the sample cylinder until it is completely full. Disconnect from the vessel being sampled. Blow off a small portion of product from the sample cylinder to allow room for expansion.
In the laboratory the cylinder is to have a helium head pressure applied of 180-200 psi. The sample cylinder is then connected to a bulkhead and then injected into the gas chromatograph. Aeropres uses a 4-port valve with a 1.0µl sample size. The instrument used is equipped with a flame ionization detector. The parameters are as follows: Oven Temp: 20-30ºC, isothermal Carrier gas: Helium 15-35cc/min. Column: 25’ x 1/8” x 0.012” wall, stainless steel, P/W 25% Bis(2-methoxylEthyl) Adipate on Chromsorb NAW, 80/100 mesh. Detector Temp: 110-225ºC Air Bottle Pressure 40-60 psig Hydrogen Flow Rate 20-30 cc/min The method used by Aeropres is a modified version of ASTM- 1954-64 The Flame Ionization detectors are calibrated monthly using only standards that are N.I.S.T. traceable.
decont055_final report addendum.doc
LP GAS CONTAMINATION REMEDIATION AT BULK TERMINALS PROJECT
FINAL REPORT ADDENDUM
Prepared for the
Propane Education & Research Council (PERC Docket #11649)
October 24, 2006
By: Nolan Sambrano, Jared Meyer, and Alex Spataru
ADEPT SCIENCE & TECHNOLOGIES, LLC 51 Rover Boulevard
Los Alamos, NM 87544 USA Telephone: (505) 672-0002
Fax: (505) 672-0003
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Table of Contents
I. Explanation of Changes to Work Originally Proposed ...................................3
A. Multi Bed Sieve vs. Activated Carbon Column...........................................3 B. Design and Calculations for Full-Scale and Pilot Columns ........................4 C. Pilot Scale vs. Full-Sized Column...........................................................4 D. Ethyl Mercaptan......................................................................................5
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I. Explanation of Changes to Work Originally Proposed This Addendum is to provide further insight into how the scope of this project evolved; how decisions were reached regarding design elements, experimental set-up, and procedures; and why certain initially intended steps were modified.
A. Multi Bed Sieve vs. Activated Carbon Column When the original proposal was written, it was not yet known what strategy would be most effective to reduce the contaminants of interest. ASCENT’s proposal references a multi-bed sieve (i.e. a column containing more than one type of adsorption media in separate layers or beds) and molecular sieve media because it was then thought that this approach would have a high likelihood of success to remove multiple contaminants. Much of the pre-award proposal was inspired by a GPA research report (#991) dated June 11, 2001. However, soon after beginning work, it was found that activated carbon had been used with some success in the past to remove heavy ends contaminants from LP Gas. The other filtering media mentioned in the same GPA report were eliminated from consideration due to characteristics less desirable for use by LP Gas bulk plant operators. Additionally, conversations with molecular sieve manufacturers regarding their use in this application were not encouraging. It became apparent from the prior work of Cosmo Engineering Co. (CEC), Phillips Petroleum Co., Petrolane, other project advisors’ experience, statements from others in the LP Gas industry, and the experience of technical experts at Calgon Carbon in removal of diesel contamination from propane, that activated carbon alone was the most promising solution to remove the contaminants of interest (i.e. heavy-ends residues). This was supported by a summary of CEC’s project results which showed that in their two-column process [one entirely of activated carbon, the other of molecular sieves (zeolite material)], the activated carbon fully removed the bulk of heavy-ends residues, while the molecular sieves removed sulfur and water. Removal of contaminants such as sulfur and water with molecular sieves is also already well characterized in the aerosol propellant industry, and not part of this project’s focus on heavy ends. At this point, it was decided that zeolite materials would not be the tested adsorbents and that using a multi-bed column would be unnecessary. While there was then consensus that activated carbon would be the way to proceed given past successes, available documentation and data from previous tests was neither accessible nor comprehensive, particularly with regards to the removal of a wide range of heavy-ends residues as opposed to simply “lube oil” or No. 4 fuel oil as in the cases of the CEC project and the data available from Mr. John O’Connor’s patent, respectively. Additionally, access to CEC’s project reports alone turned out to be prohibitively expensive (in excess of the entire PERC project budget) which was contrary to earlier expectations. Economic feasibility of field implementation was also a consideration in the selection of the particular activated carbon eventually tested.
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B. Design and Calculations for Full-Scale and Pilot Columns
The full scale column was designed and constructed after extensive research into prior work including CEC’s multi-million dollar decontamination project. This step was undertaken given earlier expectations of affordable cooperation from CEC. CEC was willing to cooperate with initial work on this project and provided basic parameters (i.e. column size and flowrates) from their prior projects. At the same time, ASCENT was working with project advisors to determine design constraints for the full-sized column. These constraints and the rationale behind their use are provided in Section VII of the Final Report. After determining the maximum sized vessel based on these constraints, and including design elements such as instrumentation ports, and a means to add and remove activated carbon, ASCENT then submitted the revised design to CEC. CEC recalculated and provided ASCENT with new estimates for the expected process flowrates. This information from CEC was considered along with project advisors’ flowrate recommendations including those of Mr. John O’Connor from prior work at Phillips Petroleum, Co. An average of these inputs was used as the target flowrate for the full-sized column and the basis for pilot-scale work. The full scale column was constructed at a time when further work with CEC appeared likely. Scaling to the smaller sized column (560:1 by volume/ 67:1 by flowrate) was a straightforward calculation to maintain the same flowrate per cross-sectional area (i.e. velocity). The dimensions, scale, flow orientation, and flow rates were then reviewed and approved by our advisors.
C. Pilot Scale vs. Full-Sized Column Prior to proceeding, the work plan (as initially conceived) was reevaluated. It is crucial to understand that prior to the two pilot plant tests, there was no first-hand knowledge that the system would work to remove the heavy-ends of interest. It was considered prudent, therefore, to use small scale tests to determine if we were on the right path. To have not done this and proceeded directly to a full sized 60-day field trial (as intended at the onset of the project) would have been extremely risky and irresponsible. By conducting well thought-out experiments at a smaller scale, ASCENT gained valuable information within the resources available to this project. Such critical path data collection would not have been possible by conducting a full-scale test as a first-and-only project step. Pilot scale work, for example, allowed for taking the column to breakthrough and exhaustion. It also allows for further development to be completed without using highly costly resources (e.g. the large volume of LP Gas needed for full-scale tests). This commonly used practice and research strategy was approved by the project advisors. Even though the size of the testing vessel was scaled down, it should be noted that the number of samples drawn and samples analyzed in these tests far exceeded the four (4) sample analyses originally proposed (17 drawn, 13 analyzed). Thus, more activated carbon heavy-ends removal data was collected than earlier anticipated.
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D. Ethyl Mercaptan The effect of this activated carbon process on ethyl mercaptan concentration, although not part of the contract, was explored in the second series of tests to provide useful data to address practical industry concerns. The results show the relative rates at which ethyl mercaptan and other contaminants elute from the column. Because analysis indicates that ethyl mercaptan is initially removed, the panel of expert advisors suggested that a cautionary statement be included. The data collected will help with both future developments of this decontamination process and to take precautionary steps, if and when they may be needed.
