{"id":1341,"date":"2012-04-01T05:00:01","date_gmt":"2012-04-01T10:00:01","guid":{"rendered":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/?p=1341"},"modified":"2012-10-23T08:16:45","modified_gmt":"2012-10-23T13:16:45","slug":"natural-gas-with-dry-ice-phase-behavior","status":"publish","type":"post","link":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/2012\/04\/natural-gas-with-dry-ice-phase-behavior\/","title":{"rendered":"Natural Gas with Dry Ice Phase Behavior"},"content":{"rendered":"

Wikipedia [1] describes dry ice as \u201cthe solid form of\u00a0carbon dioxide\u00a0(CO2<\/sub>). It is colorless, odorless, non-flammable, and slightly acidic [2]. At temperatures below\u00a0\u221269.9\u00b0F\u00a0(\u221256.6\u00b0C)\u00a0and pressures below 75.2 psia (518 kPa), the\u00a0triple point, CO2<\/sub>\u00a0changes from a solid to a gas with no intervening liquid form, through a process called\u00a0sublimation. The opposite process is called\u00a0deposition, where CO2<\/sub>\u00a0changes from the gas to solid \u00a0phase (dry ice). At atmospheric pressure, sublimation\/ <\/del>deposition occurs at\u00a0 \u2212109.3\u00b0F (\u221278.6\u00b0C). The\u00a0density\u00a0of dry ice varies, but usually ranges between about 87 and 100\u00a0lbm<\/sub>\/ft3<\/sup>\u00a0(1400\u20131600\u00a0kg\/m3<\/sup>) [3].\u00a0The low temperature and direct sublimation to a gas makes dry ice an effective\u00a0coolant, since it is colder than\u00a0water ice\u00a0and leaves no residue as it changes state [4].\u00a0Its\u00a0enthalpy of sublimation\u00a0is 245.5 Btu\/lbm<\/sub> (571 kJ\/kg).\u201d<\/p>\n

While dry ice has many good features and applications, its formation can plug up equipment and cause severe operational problems in gas processing plants. Therefore, accurate predictions of conditions for dry ice formation are required. In order to prevent dry ice formation, a good knowledge and understanding of phase behavior of systems containing carbon dioxide are essential in cryogenic gas processing as in turboexpander plants for deep natural gas liquid (NGL) recovery. Thermodynamic modeling based on the equality of chemical potentials for each component in all phases and application of an equation of state with tuned parameters is normally used for accurate prediction of dry ice formation conditions.<\/p>\n

In this tip of the month (TOTM), we will study the phase behavior of gas mixtures containing carbon dioxide. A description of phase behavior at different conditions of pressure and temperature is presented.<\/p>\n

The Peng-Robinson (PR) [5] equation of state (EOS) option of ProMax [6] was used to perform all of the calculations in this study. In dealing with dry ice, reference [7] discusses the importance of using the right tools in process simulation software. The same reference also demonstrates the accuracy of ProMax against experimental data, including GPA RR 10 experimental data [8], for prediction of dry ice formation at different conditions.<\/p>\n

Case Studies:<\/strong><\/p>\n

The composition of the two mixtures containing CO2<\/sub> considered in this study is shown in Table 1. Figure 1 also presents a simplified process flow diagram that was used to study dry ice formation in this study. \u00a0The feed gas (stream 1) enters Sep-100 from which the vapor stream (stream 2) is cooled in HEX-100. The stream leaving this cooler is passed through Sep-101 for separation of gas and liquid.<\/p>\n

Figure 2 presents a complete phase envelope for mixture A (see Table 1) in which the state of each region has been identified.<\/p>\n

The feed gas (stream 1) enters Sep-100 at -96\u02daF and 300 psia (-71.1\u02daF and 2069 kPa) which is point \u201cA\u201d on Figure 2. At this condition, it is all vapor and all of the feed leaves the separator as vapor. In the HEX-100, the vapor stream (stream 2) is cooled at constant pressure to -160\u02daF (-106.7\u02daC), which is represented by point \u201cE\u201d (stream 4). The horizontal dotted straight line identifies the cooling path. During the cooling process when point \u201cB\u201d, the dew point, on Figure 2 is reached, the first drop of liquid is formed. Between points \u201cB and C\u201d, mixture of liquid + vapor coexist at equilibrium. At point C, the incipient point of dry ice, solid phase will also form. Between points \u201cC and D\u201d, three phases of solid + liquid + vapor will coexist at equilibrium. Further cooling to point \u201cE\u201d results in a mixture of solid + liquid at equilibrium. Finally, the stream leaving this cooler is passed through Sep-101 for separation of any gas from and liquid.<\/p>\n

Table 1. The composition of the two mixture studies<\/p>\n

\"\"<\/a><\/p>\n

\"\"<\/a><\/p>\n

Figure 1. A simplified process diagram for the case study<\/p>\n

\u00a0If mixture A enters the cooler at a pressure less than 167 psia (1152 kPa) and cools down, it will form dry ice without forming any liquid. As an example, let\u2019s \u00a0assume the mixture is at\u00a0\u00a0\u00a0\u00a0 -100\u02daF and 100 psia (-73\u02daC and 690 kPa), point \u201cx\u201d on Figure 2. If this gas is cooled at constant pressure of 100 psia (690 kPa), it forms dry ice at a temperature of about -133\u02daF (-92\u02daC). Further cooling below about -137\u02daF (-94\u02daC) will form solid + liquid + vapor at equilibrium. Finally, cooling below -200 \u02daF (-129\u02daF) results in a mixture of solid + liquid in equilibrium.<\/p>\n

 <\/p>\n

\"\"<\/a><\/p>\n

Figure 2. Complete phase envelope for mixture A.<\/p>\n

 <\/p>\n

At a pressure of 300 psia (2069 kPa), starting at -90\u00b0F (-68\u00b0C) (Point \u201cA\u201d), the fluid is 100% vapor.\u00a0 Cooling at constant pressure results in liquid formation when the temperature reaches about -113\u00b0F (-81\u00b0C) at Point \u201cB\u201d.\u00a0 Further cooling results in dry ice formation at Point \u201cC\u201d and the temperature is approximately -119\u00b0F (-84\u00b0).\u00a0 The last vapor bubble would disappear at Point \u201cD\u201d (about -156\u00b0F, -104\u00b0C).\u00a0 Below this point, the fluid exists as dry ice and liquid.<\/p>\n

For the cooling process described above for a constant pressure of 300 psia, \u00a0the cooling temperature and vapor fraction of mixture as a function of heat removed from the process fluid (mixture A) in HEX-100 are shown in Figures 3A (Field Units) and 3B (SI Units).<\/p>\n

\u00a0\"\"<\/a><\/p>\n

Figure 3A. Temperature and vapor fraction of mixture A as it passes through HEX-100 (Field Units).<\/p>\n

\u00a0\"\"<\/a><\/p>\n

Figure 3B. Temperature and vapor fraction of mixture A as it passes through HEX-100 (SI Units).<\/p>\n

Each mixture has a unique phase envelope and dry ice formation curve. As the mixture composition changes, the shape of the phase envelope and the dry ice curve will change. Similarly, a complete phase envelope for mixture B with the cooling path is shown in Figures 4, 5A, and 5B.<\/p>\n

 <\/p>\n

\u00a0\"\"<\/a><\/p>\n

Figure 4. Complete phase envelope for mixture B.<\/p>\n

Conclusions:<\/strong><\/p>\n

In cryogenic processes such as turboexpander plants for deep NGL recovery, accurate prediction of dry ice formation conditions is important. A good knowledge of phase behavior and thorough understanding of dry ice formation can prevent severe operational problems. On the phase envelope, any operating condition that lies on, to the left or below the dry ice curve (the dotted black curves on Figures 2 and 4) will form a solid phase and may cause severe operational problems, damage the equipment and lead to human casualty.<\/p>\n

It is important to use the right tools and an accurate equation of state within simulation software to generate the correct phase envelope and dry ice curve. It is recommended to check the accuracy of the thermodynamic models against experimental data before generating any phase envelope or performing process simulation.<\/p>\n

 <\/p>\n

 <\/p>\n

\"\"<\/a><\/p>\n

Figure 5A. Temperature and vapor fraction of mixture B as it passes through HEX-100 (Field Units).<\/p>\n

\u00a0<\/strong><\/p>\n

To learn more about similar cases and how to minimize operational problems, we suggest attending our G40 (Process\/Facility Fundamentals<\/a>)<\/a>, G4 (<\/a>Gas Conditioning and Processing<\/a>)<\/a>, PF81 (<\/a>CO2<\/sub> Surface Facilities<\/a>)<\/a>, and PF4 (<\/a>Oil Production and Processing Facilities<\/a>)<\/a> courses.<\/p>\n

John M. Campbell Consulting (JMCC) offers consulting expertise on this subject and many others. For more information about the services JMCC provides, visit our website at\u00a0www.jmcampbellconsulting.com<\/wbr><\/a>, or email your consulting needs to\u00a0consulting@jmcampbell.com<\/a>.<\/p>\n

 <\/p>\n

By: Dr. Mahmood Moshfeghian<\/em><\/strong><\/p>\n

\u00a0\"\"<\/a><\/p>\n

Figure 5B. Temperature and vapor fraction of mixture B as it passes through HEX-100 (SI Units).<\/p>\n

\u00a0<\/em><\/p>\n

Reference:<\/strong><\/p>\n

    \n
  1. http:\/\/en.wikipedia.org\/wiki\/Dry_ice<\/a><\/li>\n
  2. Yaws, C.\u00a0Matheson gas data book<\/em>\u00a0(7th ed.). McGraw-Hill Professional. p.\u00a0982, 2001<\/li>\n
  3. H\u00e4ring, H-W.\u00a0Industrial Gases Processing<\/em>. Christine Ahner. Wiley-VCH, 2008<\/li>\n
  4. Treloar, R.,\u00a0Plumbing Encyclopedia<\/em>\u00a0(3rd ed.). Wiley-Blackwell, 2003.<\/li>\n
  5. Peng, D. Y., and Robinson, D. B., Ind. Eng. Chem. Fundam.<\/em>, Vol. 15, p. 59, 1976.<\/li>\n
  6. ProMax 3.2, Bryan Research and Engineering, Inc, Bryan, Texas, 2011.<\/li>\n
  7. Hlavinka, M. W., Hernandez, V. N., and McCartney, D., \u201cProper Interpretation of\u00a0 Freezing and\u00a0 Hydrate\u00a0 Prediction Results From Process Simulation,\u201d Proceedings of the Eighty-Fifth GPA Annual Convention. Grapevine, TX: Gas \u00a0Processors Association, 1999:121-127 GPA 2006.<\/li>\n
  8. Kurata, F., \u201cSolubility of Solid Carbon Dioxide in Pure Light Hydrocarbons and Mixtures of Light Hydrocarbons,\u201d GPA Research Report RR-10, Gas Processors Association, 1974<\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"

    Wikipedia [1] describes dry ice as \u201cthe solid form of\u00a0carbon dioxide\u00a0(CO2). It is colorless, odorless, non-flammable, and slightly acidic [2]. At temperatures below\u00a0\u221269.9\u00b0F\u00a0(\u221256.6\u00b0C)\u00a0and pressures below 75.2 psia (518 kPa), the\u00a0triple point, CO2\u00a0changes from a solid to a gas with no intervening liquid form, through a process called\u00a0sublimation. The opposite process is called\u00a0deposition, where CO2\u00a0changes from […]<\/p>\n","protected":false},"author":23,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"nf_dc_page":"","_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[3,10],"tags":[],"coauthors":[15],"class_list":["post-1341","post","type-post","status-publish","format-standard","hentry","category-gas-processing","category-process-facilities"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p1pQc4-lD","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/posts\/1341","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/users\/23"}],"replies":[{"embeddable":true,"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/comments?post=1341"}],"version-history":[{"count":3,"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/posts\/1341\/revisions"}],"predecessor-version":[{"id":1351,"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/posts\/1341\/revisions\/1351"}],"wp:attachment":[{"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/media?parent=1341"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/categories?post=1341"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/tags?post=1341"},{"taxonomy":"author","embeddable":true,"href":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/wp-json\/wp\/v2\/coauthors?post=1341"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}