{"id":2327,"date":"2016-06-06T16:13:11","date_gmt":"2016-06-06T21:13:11","guid":{"rendered":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/?p=2327"},"modified":"2016-06-06T16:13:11","modified_gmt":"2016-06-06T21:13:11","slug":"projecting-the-performance-of-adsorption-dehydration-process","status":"publish","type":"post","link":"http:\/\/www.jmcampbell.com\/tip-of-the-month\/2016\/06\/projecting-the-performance-of-adsorption-dehydration-process\/","title":{"rendered":"Projecting the Performance of Adsorption Dehydration Process"},"content":{"rendered":"

The May 2015 tip of the month<\/a> (TOTM) [1] presented a method which allows the users to estimate the decline of their adsorbent based on only one performance test run (PTR) for molecular sieve dehydrators using low pressure regeneration. This permits early formulation of a credible action plan. Site-specific factors will determines an adsorption unit\u2019s decline curve.\u00a0Consequently, conducting more than PTR is highly recommended. A poorly performing inlet separator, for example, could result in a unit exhibiting a more pronounced decline than indicated by the generic performance decline curves.<\/p>\n

One can utilize the May 2015 TOTM methodology effectively by developing a spreadsheet or a computer program. Therefore, based on this methodology, we have developed a computer module to perform all of the calculations. This computer module has been coupled with the PetroSkills\u00a0| John M Campbell GCAP (Gas Conditioning and Processing Software) [2]. This tip presents this computer model\u2019s numerical and graphical results for the same case study of May 2015 TOTM.<\/p>\n

The cyclical heating\/cooling of the adsorbent results in a capacity (mass of water per 100 mass of adsorbent) decline due to a gradual loss of crystalline structure and\/or pore closure.\u00a0 A more troublesome cause of capacity decline is contamination of the molecular sieves due to liquid carryover from the upstream separation equipment.<\/p>\n

The molecular sieve capacity decline curve is an essential element of this methodology. Figure 18.8 in Gas Conditioning and Processing, Volume 2: The Equipment Modules (9th<\/sup> Edition) [3], presents a generic molecular sieve capacity decline curves. An expanded form of Figure 18.8 with five curves is shown in Figure 1. Shown in this figure are \u201cGood\u201d, \u201cGood-Average (G_A)\u201d, \u201cAverage\u201d, \u201cAverage-Poor (A_P)\u201d, and \u201cPoor\u201d curves that are a function of site specific factors. The life of the adsorbent is a function of the number of cycles, not the elapsed calendar time. Locating one data point on Figure 1 from a performance test run (PTR) allows us to generate the decline curve of the unit in question. For computer programming purpose, we have developed a simple mathematical model. For more detail regarding adsorption dehydration process see references [1 and 3].<\/p>\n

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Figure 1.<\/strong> A generic molecular sieve capacity decline curves<\/figcaption><\/figure>\n

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

If your regeneration circuit has excess capacity over the \u201cnormal design conditions\u201d, i.e., a design factor, you have standby time. This excess capacity allows you to reduce your online adsorption time and \u201cturn the beds around\u201d faster by regenerating the beds in a shorter cycle time.\u00a0\u00a0 When you are involved in the design of an adsorption unit, it is recommended to add 10 \u2013 20% excess regeneration capacity.<\/p>\n

Because of the capacity decline curves flatten out, available standby time may be able to extend the life of a molecular sieve unit when your unit is operating on fixed cycle times.\u00a0 Other operating options include: running each cycle to water breakthrough; and, reducing the cycle times in discreet steps throughout the life of the adsorbent.<\/p>\n

To demonstrate application of the developed program and illustrate the benefits of standby time we considered the same case study as in the May 2015 TOTM [1]. As shown in Figure 2, a natural gas processing plant has commissioned a new 3 tower molecular sieve dehydration unit to process 11.3 x 106 <\/sup>std m3<\/sup>\/d (400 MMscfd) prior to flowing to a deep ethane recovery unit.\u00a0 The unit is expected to run for 3 years before needing a recharge and the plant turnaround is based on this expectation.\u00a0 The following assumptions are made:<\/p>\n