Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
  • C09K5/02—Materials undergoing a change of physical state when used
  • C09K5/04—Materials undergoing a change of physical state when used the change of state being from liquid to vapour or vice versa
  • C09K5/047—Materials undergoing a change of physical state when used the change of state being from liquid to vapour or vice versa for absorption-type refrigeration systems

Definitions

• This invention relates to solution compositions which absorb and desorb useful quantities of water vapor at high boiling point elevation, and are useful in absorption cycle devices such as heat pumps.
• the solution and the absorption cycles which employ it are particularly advantageous at high temperatures, e.g., up to 260°C and even higher.
• the main function of any heat pump is to raise the temperature of a supply of heat. In an absorption cycle heat pump, this is caused to occur by lowering the temperature of another quantity of heat.
• the heat that is to be raised in temperature is applied to a boiler
• the absorber and evaporator operate at approximately the same pressure, and the generator and condenser also operate at about the same pressure, but one which is substantially different from the absorber/evaporator pressure, liihen the generator/condenser pressure is higher than the absorber/evaporator pressure
• the cycle is the conventional one found in refrigerators and air conditioners, and is herein called forward cycle: heat is input at the two temperature extremes, and is delivered at midpoint temperatures.
• the resulting cycle is herein called reverse cycle: heat is input at mid temperatures, and is rejected at both the highest cycle temperature and the lowest cycle temperature. Both cycles are k ⁇ ow ⁇ in the prior art—see for example U.S. patents 4350571 and 4402795.
• the amount of temperature increase provided by an absorption heat pump is thus seen to be determined by the boiling point elevation of the absorbent solution.
• the net lift realized will be the boiling point elevation minus the heat exchanger temperature differentials; thus, practical machines require boiling point elevations on the order of 30°C or more.
• the absorbent solution transport the workirig medium from the absorber to the generator.
• the absorbent solution must have an acceptably large carrying capacity for the working medium at the high boiling point elevation condition, as otherwise excessively high solution circulation rates (and attendant high solution heat exchanger heat losses) would be experienced.
• the carrying capacity is proportional to the derivative of the solution concentration with respect to the boiling point elevation, and this is the quantity which must be acceptably large at high boiling point elevations.
• the absorbent solution should be reasonably noncorrosive such that ordinary materials of construction can be used; it should not thermally degrade or decompose at high use temperatures; it must not freeze or crystallize at normally encountered use conditions; it should have acceptable liquid properties such as low viscosity for pumping, minimal foaming tendency, easily boil, etc: it should be relatively non toxic, ⁇ on explosive, and nonflammable; it should be reasonably available; and it should have a low vapor pressure so as not to require rectification, as in NH 3 -H 2 O systems.
• the desired and unexpectedly advantageous absorption solution properties are obtained from a composition of matter comprised of at least 35 mole percent LiNO 3 and at least 35 mole percent alkali nitrite.
• the composition is normally employed in aqueous solution at concentrations containing between 2 and 50 weight percent H 2 O.
• the high Li content provides high carrying capacity at high boiling point elevations, whereas the approximately equal nitrate and nitrite content lowers the melting point of both the anhydrous and aqueous solution.
• the composition is particularly useful in absorption cycles operating at high temperatures, e.g., up to 260°C or higher, and is applicable to all cycle variations: forward or reverse cycle, multieffect generators or absorbers, etc. Best Mode for Carrying Out the Invention
• Example 1 A composition consisting ⁇ f 50 weight percent LiNO 3 , 30 weight percent NaNO 2 , and 20 weight percent KNO 2 was tested for boiling point elevation and carrying capacity. The respective mole percentages are approximately 52, 31, and 17%. The following results mere obtained, as a function of solution concentration (i.e., the weight percent nonaqueous component, wher ⁇ the balance is H 2 O):
• the solution provides acceptable carrying capacity (e.g., is reasonably dilute) out t ⁇ boiling point elevations of at least 50 or 60°C. Also, comparable concentrations give comparable boiling point elevations at any pressure.
• composition in anhydrous form turns very viscous and begins to freeze at about 106°C, but is liquid to much lower temperatures in aqueous form.
• a composition of 50 mole percent LiNO 3 , 25 mole percent LiNO 2 , and 25 mole percent l ⁇ laNO 2 provides even greater carrying capacity (i.e., more dilute solutions) at comparable boiling point elevations than does the Example 1 mixture.
• it introduces two disadvantages— it has a higher melting point, and, hence, is susceptible to freezing, particularly during cooldown and shutdown. This can be counteracted by providing a reservoir of dilution water which is added to the solution during shutdown, then boiled out and separately condensed and stored during startup. An oversize condenser would also accomplish this, by providing a controllable liquid drain valve. This technique applies equally to other compositions, e.g., the, Example 1 composition.
• the alkali nitrites, and particularly LiNO 2 are susceptible to carbo ⁇ ation from CO 2 .
• the solution and the entire absorption cycle should be hermetically sealed, as is common practice with LiBr units.
• lithium halides e.g., LiBr or LiCl
• Certain organic additives e.g., glycols or alcohols, will lower the melting point.
• Other additives may promote boiling, decrease foaming tendency, etc. In general, additions up to 30 weight percent are acceptable when not precluded by the intended use temperature.
• an aqueous absorbent solution which may be exposed to temperatures appreciably above 200°C or lower, and in which the nonaqueous component is comprised of at least 35 mole percent lithium nitrate, it is preferable to constitute the bulk of the remainder of the nonaqueous component from sodium nitrate and potassium nitrate, so as to exclude nitrite anion from the solution, while still allowing for minor amounts of other beneficial additives which may for example inhibit foaming or enhance heat transfer.
• an aqueous solution in which the nonaqueous component is comprised of approximately 55 m/o LiNO 3 , 25 m/o KNO 3 , and 20 m/o NaNO 3 constitutes a particularly desirable composition for absorbing water vapor at higher temperatures.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Combustion & Propulsion (AREA)
• Thermal Sciences (AREA)
• Physics & Mathematics (AREA)
• Organic Chemistry (AREA)
• Sorption Type Refrigeration Machines (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)
• Cell Electrode Carriers And Collectors (AREA)
• Secondary Cells (AREA)
• Battery Electrode And Active Subsutance (AREA)

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• 1982
  • 1982-09-29 US US06/428,483 patent/US4454724A/en not_active Expired - Fee Related
• 1983
  • 1983-09-28 EP EP83903445A patent/EP0120085B1/en not_active Expired
  • 1983-09-28 JP JP58503480A patent/JPS59501750A/ja active Granted
  • 1983-09-28 AU AU21264/83A patent/AU566179B2/en not_active Ceased
  • 1983-09-28 WO PCT/US1983/001502 patent/WO1984001422A1/en not_active Ceased
  • 1983-09-28 DE DE8383903445T patent/DE3376675D1/de not_active Expired

Patent Citations (2)

Non-Patent Citations (1)

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