Method for semi-continuous heat exchange operations by alternating between heat exchangers
A method for semi-continuous operation of a heat exchange process that alternates between two heat exchangers is disclosed. The method comprises, first, providing a contact liquid to a first heat exchanger while the second heat exchanger is on standby. The contact liquid contains a dissolved gas, an entrained gas, or residual small particles that foul the first heat exchanger by condensing or depositing as a foulant onto the first heat exchanger, restricting free flow of the contact liquid. Second, detecting a pressure drop across the first heat exchanger. Third, switching flows of the coolant from the first to the second heat exchanger. Fourth, removing the foulant from the now standby first heat exchanger by providing heat to the heat exchanger, passing a non-reactive gas through the heat exchanger, or a combination thereof. In this manner, the heat exchange process operates semi-continuously.
1. A method for semi-continuous operation of a heat exchange process that alternates between a first heat exchanger and a second heat exchanger, the method comprising:
i) providing a contact liquid to the first heat exchanger and cooling the contact liquid via heat exchange with a coolant while the second heat exchanger is on standby, wherein being on standby means the second heat exchanger is ready to take over operation of the first heat exchanger upon demand; wherein the contact liquid contains a dissolved gas, an entrained gas, or residual small particles that foul the first heat exchanger by condensing or depositing as a foulant onto at least a portion of any interior walls of the first heat exchanger that contact the contact liquid, restricting free flow of the contact liquid;
ii) operating the first heat exchanger while the second heat exchanger is on standby, a pressure drop across the first heat exchanger caused by the foulant, the first heat exchanger operating while the second heat exchanger is on standby;
iii) stopping flow of the coolant to the first heat exchanger and beginning flow of the contact liquid to the second heat exchanger, then stopping flow of the contact liquid to the first heat exchanger and beginning flow of the coolant to the second heat exchanger, thereby causing the second heat exchanger to switch from standby to operation and removing the first heat exchanger from operation to standby; and,
iv) removing the foulant from the now standby first heat exchanger by a process comprising:
a. providing heat to the portion of the interior walls of the heat exchanger where the foulant is condensed,
b. passing a non-reactive gas across the portion of the interior walls of the heat exchanger where the foulant is condensed; or,
c. a combination of the above;
wherein the first heat exchanger and the second heat exchanger thereby switch roles from standby to operating, with steps i to iv repeated with reversed roles; whereby the heat exchange process operates semi-continuously.
2. The method of claim 1 , wherein the foulant comprises carbon dioxide, nitrogen oxide, sulfur dioxide, nitrogen dioxide, sulfur trioxide, hydrogen sulfide, mercury, entrained particulate, hydrogen cyanide, impurities of burned fuel, byproducts of burned fuel, or a combination thereof.
3. The method of claim 1 , wherein the contact liquid comprises 1,1,3-trimethylcyclopentane, 1,4-pentadiene, 1,5-hexadiene, 1-butene, 1-methyl-1-ethylcyclopentane, 1-pentene, 2,3,3,3-tetrafluoropropene, 2,3-dimethyl-1-butene, 2-chloro-1,1,1,2-tetrafluoroethane, 2-methylpentane, 3-methyl-1,4-pentadiene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-methylpentane, 4-methyl-1-hexene, 4-methyl-1-pentene, 4-methylcyclopentene, 4-methyl-trans-2-pentene, bromochlorodifluoromethane, bromodifluoromethane, bromotrifluoroethylene, chlorotrifluoroethylene, cis 2-hexene, cis-1,3-pentadiene, cis-2-hexene, cis-2-pentene, dichlorodifluoromethane, difluoromethyl ether, trifluoromethyl ether, dimethyl ether, ethyl fluoride, ethyl mercaptan, hexafluoropropylene, isobutane, isobutene, isobutyl mercaptan, isopentane, isoprene, methyl isopropyl ether, methylcyclohexane, methylcyclopentane, methylcyclopropane, n,n-diethylmethylamine, octafluoropropane, pentafluoroethyl trifluorovinyl ether, propane, sec-butyl mercaptan, trans-2-pentene, trifluoromethyl trifluorovinyl ether, vinyl chloride, bromotrifluoromethane, chlorodifluoromethane, dimethyl silane, ketene, methyl silane, perchloryl fluoride, propylene, vinyl fluoride, or combinations thereof.
4. The method of claim 1 , wherein the coolant comprises liquid nitrogen, ethane, methane, propane, refrigerants, or combinations thereof.
5. The method of claim 1 , wherein the first heat exchanger and second heat exchanger comprise brazed plate, aluminum plate, shell and tube, plate, plate and frame, plate and shell, or plate fin style heat exchangers.
6. The method of claim 5 , wherein the first heat exchanger and second heat exchanger are shell and tube style heat exchangers, containing a shell enclosing a tube, wherein the tube has a varying diameter.
7. The method of claim 1 , wherein the non-reactive gas comprises nitrogen, methane, argon, or combinations thereof.
8. The method of claim 1 , wherein the non-reactive gas is pre-heated and moisture removed by passing the non-reactive gas across a desiccant.
9. The method of claim 1 , wherein the heat provided to the interior walls of the first heat exchanger is provided by heating elements attached to the heat exchanger.
10. The method of claim 9 , wherein the heating elements are attached to an exterior wall of the first heat exchanger.
11. The method of claim 10 , wherein the contact liquid travels through the exterior elements of the first heat exchanger.
12. The method of claim 9 , wherein the contact liquid travels through interior elements of the first heat exchanger, and wherein the heating elements are attached to the outside of the interior elements.
13. The method of claim 12 , wherein the heating elements are comprised of piezoelectric heaters, heat trace tape, heat trace sheets, band heaters, or combinations thereof.
14. The method of claim 12 , wherein the heating elements are located at the inlet and outlet of the interior elements to the first heat exchanger, and wherein the heating elements warm only the portion of the interior elements that extend out of the first heat exchanger, wherein heat is conducted along the interior elements.
15. The method of claim 9 , wherein the heating elements are attached to the inside of the interior elements.
16. The method of claim 9 , wherein, after stopping flow of the contact liquid to the first heat exchanger, the connections to the interior elements by external piping are disconnected and the heating elements are inserted into the inside of the interior elements.
17. The method of claim 1 , wherein the contact liquid travels through interior elements of the first heat exchanger, and wherein the heat provided to the interior walls of the first heat exchanger is provided by passing a warm fluid through the outer elements of the heat exchanger.
18. The method of claim 17 , wherein the warm fluid comprises air, nitrogen, carbon dioxide, argon, or combinations thereof.
19. The method of claim 17 , wherein the warm fluid comprises water, 1,1,3-trimethylcyclopentane, 1,4-pentadiene, 1,5-hexadiene, 1-butene, 1-methyl-1-ethylcyclopentane, 1-pentene, 2,3,3,3-tetrafluoropropene, 2,3-dimethyl-1-butene, 2-chloro-1,1,1,2-tetrafluoroethane, 2-methylpentane, 3-methyl-1,4-pentadiene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-methylpentane, 4-methyl-1-hexene, 4-methyl-1-pentene, 4-methylcyclopentene, 4-methyl-trans-2-pentene, bromochlorodifluoromethane, bromodifluoromethane, bromotrifluoroethylene, chlorotrifluoroethylene, cis 2-hexene, cis-1,3-pentadiene, cis-2-hexene, cis-2-pentene, dichlorodifluoromethane, difluoromethyl ether, trifluoromethyl ether, dimethyl ether, ethyl fluoride, ethyl mercaptan, hexafluoropropylene, isobutane, isobutene, isobutyl mercaptan, isopentane, isoprene, methyl isopropyl ether, methylcyclohexane, methylcyclopentane, methylcyclopropane, n,n-diethylmethylamine, octafluoropropane, pentafluoroethyl trifluorovinyl ether, propane, sec-butyl mercaptan, trans-2-pentene, trifluoromethyl trifluorovinyl ether, vinyl chloride, bromotrifluoromethane, chlorodifluoromethane, dimethyl silane, ketene, methyl silane, perchloryl fluoride, propylene, vinyl fluoride, or combinations thereof.
20. The method of claim 19 , wherein the heating elements are comprised of piezoelectric heaters, heat trace tape, heat trace sheets, or combinations thereof.