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.
What is claimed is:
1. 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.
2. Method of claim 1 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.
3. Method of claim 1 wherein said tablets comprise 2% to 3% potassium
4. Method of claim 1 wherein said gas is natural gas.
5. Method of claim 1 wherein said tablets include desiccant salts.
6. Method of claim 5 wherein said desiccant salts comprise predominantly
7. Method of claim 1 wherein said separating is accomplished by
8. Method of claim 1 followed by replacing said bed of tablets
with new tablets comprising solid potassium formate.
9. Method of claim 8 followed by another iteration of the method
of claim 1.
10. Method of claim 5 wherein said desiccant salts include lithium
11. Method of claim 5 wherein said desiccant salts include cesium
12. Method of claim 1 wherein contacting of said gas with said
bed of tablets is accomplished by flowing said gas upwardly through
said bed of tablets.
13. 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.
14. A deliquescent tablet of claim 13 wherein the potassium formate
comprises about 2% to about 3% by weight.
15. A deliquescent tablet of claim 14 comprising about 0.5% to
about 97% calcium chloride.
16. 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.
17. A desiccant tablet of claim 16 made by compression, wherein
said surfactant is sodium lauryl sulfonate.
18. A desiccant tablet of claim 16 wherein said at least one desiccant
salt comprises calcium chloride.
19. A desiccant tablet of claim 16 wherein said potassium formate
comprises 2-3% by weight of said tablet.
Tablets containing potassium formate are useful for drying gases
because of their deliquescent properties.
BACKGROUND OF THE INVENTION
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.
An early patent to, Hutchinson, U.S. Pat. No. 2804940 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. 2143008
and by Thomas in U.S. Pat. No. 5733841; see also Thomas U.S. Pat.
No. 5766309 for a good illustration of the placement of the solid
deliquescent materials in a contemporary drying vessel; this patent
(U.S. Pat. No. 5766309) is incorporated by reference herein in
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. 5846450.
SUMMARY OF THE INVENTION
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.
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
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.
In Table 1 and elsewhere herein, CaCl2 77% is calcium chloride
containing 23% moisture. 10% KCOOH means 77%CaCl.sub.2 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.
TABLE 1 Weight increase over time (grams) Product 3 hours 18 hours
25 hours 90 hours CaCl2 77% 0.7295 4.609 6.5831 19.5703 CaCl2 77%
0.4096 3.2685 4.5123 17.9454 +10% KCOOH 0.6026 6.0434 7.6411 19.6084
+10% KCOOH 0.781 5.8817 7.7085 22.1131 94% + 10% KF 0.002 4.5483
5.6003 16.0585 94% + 10% KF 0.0931 3.2718 4.294 16.8932
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
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.
TABLE 3 Weight Increase Over Time (grams) Hours Product 16 hrs
20 hrs 24 hrs 40 hrs 77% CaCl2 6.547 8.5854 9.5619 15.3974 94% CaCl2
+ 5% NH4F 4.964 6.3635 7.2397 12.9733 94% CaCl2 + 7.5% NH4F 8.2826
10.3386 11.3232 15.2833 94% CaCl2 + 10% NH4F 6.4756 8.0257 9.0649
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
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% KCOOH 3.9704 11.7115 13.8077 17.9961 19.2392 21.8174 +5.0%
KCOOH 3.8633 11.5287 14.0292 17.9577 19.0072 21.1031 +7.5% KCOOH
4.8065 10.7662 13.1887 16.4462 17.7821 19.7666 +10.0% KCOOH 4.7849
10.0518 12.7825 15.8435 17.2899 18.937
For or 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.
TABLE 6 Weight Increase Over Time 4 hrs 8 hrs 24 hrs 28 hrs 48
hrs 94% CaCl2 + 10% NaCl 0.8145 2.1562 8.3738 9.5873 15.6393 94%
CaCl2 + 20% NaCl 1.4649 2.6146 8.4068 9.303 14.9175 100% KCOOH +
20% NaCl 2.0998 3.8347 10.8299 12.3011 15.5572 100% KCOOH + 20%
NaCl 1.3877 2.6183 9.3758 11.2575 14.1278 94% CaCl.sub.2 + 20% CaBr.sub.2
0.8164 1.5235 6.7693 7.7308 13.4968
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.
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.
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.
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.
TABLE 7 Meter pressure 611 612 621 631 Gas flow rate (MMscfd) 1.19
1.183 1.071 0.97 Inlet temperature (.degree. F.) 68 80 90 100 Inlet
gas moisture (lbs H.sub.2 O/MMscfd) Sat. Sat. Sat. Sat. Outlet gas
moisture (lbs H.sub.2 O/MMscfd) Tablet A 5.0 5.8 6.4 11.0 Tablet
Z 2.9 4.9 5.7 6.1
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.