Desiccant tablets for gas drying

Information

  • Patent Application
  • 20020083832
  • Publication Number
    20020083832
  • Date Filed
    November 09, 2001
    23 years ago
  • Date Published
    July 04, 2002
    22 years ago
Abstract
Desiccant tablets including solid potassium formate are used to dry gas, especially in natural gas transmission lines. Preferred tablets comprise 1-4% potassium formate (most preferably 2-3%), up to 1% of a surfactant as a lubricant, and the balance desiccant salts, preferably calcium chloride.
Description


TECHNICAL FIELD

[0002] Tablets containing potassium formate are useful for drying gases because of their deliquescent properties.



BACKGROUND OF THE INVENTION

[0003] In the past, desiccants have been commonly used to dry gases such as natural gas, particularly for its transmission through pipelines. Typically the pipelines carry natural gas over hundreds of miles, and it is necessary and desirable to remove whatever moisture is present in the gas and/or in the pipeline. To this end, the art has employed common desiccant salts such as calcium chloride, made into tablets which tend to absorb the moisture.


[0004] An early patent to Hutchinson, U.S. Pat. No. 2,804,940, suggests passing a partially dehydrated natural gas upwards through a bed of solid particulate deliquescent material such as calcium, magnesium, or lithium chloride, or mixtures of them. Certain molar ratios of chlorides and bromides are suggested by Heath in U.S. Pat. No. 2,143,008 and by Thomas in U.S. Pat. No. 5,733,841; see also Thomas U.S. Pat. No. 5,766,309. for a good illustration of the placement of the solid deliquescent materials in a contemporary drying vessel; this patent (U.S. Pat. No. 5,766,309) is incorporated by reference herein in its entirety.


[0005] A solution of 40-70% potassium formate is suggested for use as a moisture absorbent in dehumidifiers and similar devices by Atkinson in U.S. Pat. No. 5,846,450.



SUMMARY OF THE INVENTION

[0006] Tablets are made of powdered or crystalline potassium formate and used to remove moisture from gases such as natural gas. The tablets may contain from 0.5% to 100% by weight potassium formate, the balance being alkali or alkaline earth metal formates (preferably sodium, calcium, cesium and/or magnesium formate), chlorides and/or bromides (preferably calcium chloride, potassium chloride, cesium chloride, lithium chloride, or mixtures thereof). The tablet is preferably made under compression and, for use in gas dryers in natural gas transmission lines, preferably weighs about 7 to 15 grams so it can conveniently form a bed in a more or less conventional gas dryer. A pillow shape is convenient, but no particular shape is required for this invention. Preferred tablets comprise 97.5% calcium chloride and 2.5% potassium formate. An additional 0.5% of a binder, which is preferably sodium lauryl sulfonate, may also be used. The preferred tablets need not use these exact proportions, however—they may comprise 0.5% to 100% potassium formate, an additional 0.01% by weight to 1% by weight of a surfactant used as a lubricant, and the balance one or more alkali metal or alkaline earth metal halides.


[0007] Tablets made as described above and containing 1-4% potassium formate, most preferably 2-3% potassium formate, are particularly advantageous not only for their gas drying abilities but also because recrystallization in the sump is minimal or nonexistent.







DETAILED DESCRIPTION OF THE INVENTION

[0008] Comparisons have been made of the tablets of the present invention, containing potassium formate, to various tablets containing calcium chloride. For the comparisons, tablets were made of each of the materials indicated. Tablets of each description were placed in a screen basket which in turn was placed in a humidifier and permitted to remove moisture from the same air. The baskets retained the tablets but permitted liquid to drain into a pan. The pans were preweighed and weighed again periodically. Results are reported in terms of weight gain (liquid) in the pans, in grams, over time. Table I presents the data obtained.


[0009] In Table 1 and elsewhere herein, CaCl2 77% is calcium chloride containing 23% moisture. 10%KCOOH means 77%CaCl2 having an additional (based on the calcium chloride) 10% potassium formate. “94%+10%KF” means, in flake form, 94% calcium chloride, 6% moisture and an additional 10% potassium formate based on the calcium chloride and moisture.
1TABLE 1Weight increase over time (grams)Product3 hours18 hours25 hours90 hoursCaCl2 77%0.72954.609 6.583119.5703CaCl2 77%0.40963.26854.512317.9454+10% KCOOH0.60266.04347.641119.6084+10% KCOOH0.781 5.88177.708522.113194% + 10% KF0.002 4.54835.600316.058594% + 10% KF0.09313.27184.294 16.8932


[0010]

2





TABLE 2










Weight increase over time (grams)











Product
16 hours
20 hours
24 hours
40 hours





CaCl2 77%
8.9011
9.6635
10.0889 
12.4836


94% + 2.5% KF
6.9944
8.4999
9.5212
14.1517


94% + 5.0% KF
8.245 
9.0611
9.6312
12.8922


94% + 7.5% KF
7.8536
8.7734
9.9184
13.9462


94% + 10% KF
7.259 
8.1575
9.1607
13.2313










[0011] In Table 2, “94%+10%KF” means 94% calcium chloride, 6% moisture and an additional 10% potassium formate based on the calcium chloride and moisture. “2.5%KF” “5%KF,” and “7.5%KF” mean the indicated percentages of potassium formate in addition to the 94% calcium chloride. In Table 3, the term NH4F means ammonium formate.
3TABLE 3Weight Increase Over Time (grams)HoursProduct16 hrs20 hrs24 hrs40 hrs77% CaCl26.547 8.58549.561915.397494% CaCl2 + 5% NH4F4.964 6.36357.239712.973394% CaCl2 + 7.5% NH4F8.282610.3386 11.3232 15.283394% CaCl2 + 10% NH4F6.47568.02579.064913.1451


[0012]

4





TABLE 4










Weight Increase Over Time











2 hours
5 hours
24 hours
















LiCl
0.2913
1.8077
9.8172



KCOOH
0.5877
2.2647
9.993 



77% CaCl2
0.0111
0.4246
4.9159



Sm. Mesh CaCl2
0.2023
0.5881
4.9159



Prilled CaCl2
0.0991
0.7136
4.6106











[0013]

5





TABLE 5










Weight Increase Over Time














7 hrs
22 hrs
29 hrs
46 hrs
53 hrs
70 hrs

















77% CaCl2
2.7918
10.2764
12.082
15.7432
16.809
19.0542


+2.5%
3.9704
11.7115
13.8077
17.9961
19.2392
21.8174


KCOOH


+5.0%
3.8633
11.5287
14.0292
17.9577
19.0072
21.1038


KCOOH


+7.5%
4.8065
10.7662
13.1887
16.4462
17.7821
19.7666


KCOOH


+10.0%
4.7849
10.0518
12.7825
15.8435
17.2899
18.937


KCOOH










[0014] For Table 5, the indicated percentages of potassium formate were added to the standard 77% calcium chloride, which contained 23% by weight moisture at the beginning of the test.
6TABLE 6Weight Increase Over Time4 hrs8 hrs24 hrs28 hrs48 hrs94% CaCl2 +0.81452.15628.37389.587315.639310% NaCl94% CaCl2 +1.46492.61468.40689.30314.917520% NaCl100% KCOOH +2.09983.834710.829912.301115.557220% NaCl100% KCOOH +1.38772.61839.375811.257514.127820% NaCl94% CaCl2 +0.81641.52356.76937.730813.496820% CaBr2


[0015] For Table 6, the indicated additions of sodium chloride and calcium bromide were made to 94% calcium chloride in the case of the first, second and fifth tests, and to a 100% aqueous solution of potassium formate in the third and fourth tests.


[0016] In each case where potassium formate was present, the formation of the drained solution was faster than with compositions not including potassium formate. Potassium formate clearly absorbs more moisture, more readily, than the other salts tested, and clearly enhances these abilities for any of the solution combinations.


[0017] Thus it will be seen that my invention comprises a deliquescent gas drying tablet comprising 0.5% to 100% solid potassium formate and 0% to 99.5% alkali, alkaline earth metal or ammonium formates, chlorides, bromides or mixtures thereof. The composition is preferably comprises about 5% to about 99.5% by weight potassium formate and most preferably about 5% to about 15% potassium formate with the balance being desiccant salts such as alkali (including cesium), alkaline earth metal or ammonium formates, chlorides, bromides or mixtures thereof, with calcium chloride being preferred.


[0018] Following in Table 7 is a comparison of a tablet of the present invention, comprising 77% calcium chloride, 2.5% potassium formate, and water (Tablet Z), to a tablet containing no potassium formate—that is, comprising 77% calcium chloride and water (Tablet A). All four tests were conducted at the same natural gas line site.
7TABLE 7Meter pressure611612621631Gas flow rate (MMscfd)1.191.1831.0710.97Inlet temperature (° F.)688090100Inlet gas moistureSat.Sat.Sat.Sat.(lbs H2O/MMscfd)Outlet gas moisture(lbs H2O/MMscfd)Tablet A5.05.86.411.0Tablet Z2.94.95.76.1


[0019] Tablet Z, containing 2.5% potassium formate, was not only clearly superior in drying the gas, but also showed no signs of recrystallizing in the sump, in contrast to liquid generated by Tablet A.


Claims
  • 1. A deliquescent gas drying tablet comprising 0.5% to 100% solid potassium formate and 0% to 99.5% alkali, alkaline earth metal or ammonium formates, chlorides, bromides or mixtures thereof.
  • 2. A deliquescent tablet of claim 1 wherein the potassium formate comprises about 5% to about 99.5% by weight.
  • 3. A deliquescent tablet of claim 2 comprising about 0.5% to about 95% calcium chloride.
  • 4. A deliquescent tablet of claim 1 wherein the potassium formate comprises 5% to 95% by weight of said tablet.
  • 5. A deliquescent tablet of claim 1 wherein the potassium formate comprises 5% to 15% of said tablet.
  • 6. Method of drying gas comprising contacting gas with a bed of tablets comprising potassium formate thereby forming an aqueous solution of potassium formate comprising water from said gas and potassium formate from said tablet, and separating said solution from said bed of tablets.
  • 7. Method of claim 6 wherein at least some of said solution is permitted to remain in contact with said bed of tablets and to contact said gas, whereby said solution continues to remove moisture from said gas until said tablets are substantially dissolved.
  • 8. Method of claim 6 wherein said tablets comprise 5% to 99.5% potassium formate.
  • 9. Method of claim 8 wherein said tablets comprise about 5% to about 15% potassium formate and the balance is desiccant salts.
  • 10. Method of claim 6 wherein said gas is natural gas.
  • 11. Method of claim 9 wherein said balance of desiccant salts comprise predominantly calcium chloride.
  • 12. Method of claim 6 wherein said separating is accomplished by draining.
  • 13. Method of claim 7 followed by replacing said bed of tablets with new tablets comprising solid potassium formate.
  • 14. Method of claim 13 followed by another iteration of the method of claim 13.
  • 15. Method of claim 9 wherein said desiccant salts include lithium chloride.
  • 16. Method of claim 9 wherein said desiccant salts include cesium chloride.
  • 17. Method of claim 6 wherein contacting of said gas with said bed of tablets is accomplished by flowing said gas upwardly through said bed of tablets.
  • 18. A desiccant tablet comprising about 5% to about 15% by weight potassium formate, about 0.1 to 1% surfactant, and the balance at least one desiccant salt.
  • 19. A desiccant tablet of claim 18 made by compression, wherein said surfactant is sodium lauryl sulfonate.
  • 20. A desiccant tablet of claim 18 wherein said at least one desiccant salt comprises calcium chloride.
  • 21. A deliquescent gas drying tablet comprising 1% to 4% solid potassium formate and 0% to 99% alkali, alkaline earth metal or ammonium formates, chlorides, bromides or mixtures thereof.
  • 22. A deliquescent tablet of claim 21 wherein the potassium formate comprises about 2% to about 3% by weight.
  • 23. A deliquescent tablet of claim 22 comprising about 0.5% to about 97% calcium chloride.
  • 24. Method of drying gas comprising contacting gas with a bed of tablets comprising 1-4% potassium formate by weight thereby forming an aqueous solution comprising water from said gas and potassium formate from said tablet, and separating said solution from said bed of tablets.
  • 25. Method of claim 24 wherein at least some of said solution is permitted to remain in contact with said bed of tablets and to contact said gas, whereby said solution continues to remove moisture from said gas until said tablets are substantially dissolved.
  • 26. Method of claim 24 wherein said tablets comprise 2% to 3% potassium formate.
  • 27. Method of claim 24 wherein said gas is natural gas.
  • 28. Method of claim 24 wherein said tablets include desiccant salts.
  • 29. Method of claim 28 wherein said desiccant salts comprise predominantly calcium chloride.
  • 30. Method of claim 24 wherein said separating is accomplished by draining.
  • 31. Method of claim 24 followed by replacing said bed of tablets with new tablets comprising solid potassium formate.
  • 32. Method of claim 31 followed by another iteration of the method of claim 24.
  • 33. Method of claim 28 wherein said desiccant salts include lithium chloride.
  • 34. Method of claim 28 wherein said desiccant salts include cesium chloride.
  • 35. Method of claim 24 wherein contacting of said gas with said bed of tablets is accomplished by flowing said gas upwardly through said bed of tablets.
  • 36. A desiccant tablet comprising about 1% to about 4% by weight potassium formate, about 0.1 to 1% surfactant, and the balance at least one desiccant salt.
  • 37. A desiccant tablet of claim 18 made by compression, wherein said surfactant is sodium lauryl sulfonate.
  • 38. A desiccant tablet of claim 18 wherein said at least one desiccant salt comprises calcium chloride.
  • 39. A desiccant tablet of claim 36 wherein said potassium formate comprises 2-3% by weight of said tablet.
RELATED APPLICATION

[0001] This application is a continuation-in-part of my application of the same title filed Mar. 9, 2001, Ser. No. 09/803,072, which is based upon and incorporates the entire disclosure and claims of my Provisional Application Serial No. 60/217,805 filed Jul. 12, 2000.

Provisional Applications (1)
Number Date Country
60217805 Jul 2000 US
Continuation in Parts (1)
Number Date Country
Parent 09803072 Mar 2001 US
Child 10037825 Nov 2001 US