Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
  • B01D3/007—Energy recuperation; Heat pumps
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F22—STEAM GENERATION
  • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
  • F22B3/00—Other methods of steam generation; Steam boilers not provided for in other groups of this subclass
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B27/00—Machines, plants or systems, using particular sources of energy
  • F25B27/02—Machines, plants or systems, using particular sources of energy using waste heat, e.g. from internal-combustion engines
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B29/00—Combined heating and refrigeration systems, e.g. operating alternately or simultaneously
  • F25B29/006—Combined heating and refrigeration systems, e.g. operating alternately or simultaneously of the sorption type system
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
  • Y02A30/00—Adapting or protecting infrastructure or their operation
  • Y02A30/27—Relating to heating, ventilation or air conditioning [HVAC] technologies
  • Y02A30/274—Relating to heating, ventilation or air conditioning [HVAC] technologies using waste energy, e.g. from internal combustion engine
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
  • Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
  • Y02B30/52—Heat recovery pumps, i.e. heat pump based systems or units able to transfer the thermal energy from one area of the premises or part of the facilities to a different one, improving the overall efficiency

Definitions

• SOLUTION HEAT PUMP APPARATUS AND METHOD This invention relates to solution heat pump systems and to methods for utilizing waste heat and more particularly to waste heat powered solution heat pump applications to up-grade waste heat by temperature boosting for use in various industrial applications for producing steam.
• This invention also relates to improvements in the heat exchanger apparatus in solution heat pump systems and in particular to apparatus and methods for improving the efficiency of heat exchange in the desorber and absorber in a waste heat powered solution heat pump application to up-grade waste heat by temperature boostin .
• Many solution heat pump apparatus and methods have been developed.
• One of the first proposed practical uses of an absorption heat pump was reported by D.A. Williams and J. B. Tredemann at the Intersociety Energy Conversion Engineering Conference, 9th Proceedings, August, 1974 in a paper entitled Heat Pump Powered by Natural Thermal Gradients.
• waste heat from industrial or other sources can be boosted to higher temperature levels by combining at least one relatively high pressure Rankine vapor generation cycle with at least one solution heat pump cycle.
• waste heat is utilized to boil off a fluid termed a refrigerant in the Rankine cycle evaporator to provide a source of vapor to an absorber in the solution heat pump.
• the refrigerant vapor is contacted with a binary working solution containing absorbent and refrigerant.
• the refrigerant vapor is absorbed into the binary absorbent solution, its latent heat of condensation and heat of solution are given off to a heat exchanger at a temperature higher than the temperature of the waste heat source.
• the work- ing solution is then throttled to reduce the pressure and introduced into a relatively low pressure desorber where a portion of the refrigerant is desorbed as vapor from the binary solution by the addition of more waste heat through a heat exchanger.
• the desorbed refrigerant vapor is then condensed by contact with a colder heat exchanger at a temperature less than the temperature of the vapor, and the condensed refrigerant is then pumped to the evaporator for reuse.
• the concentrated working solution is recycled from the desorber to the absorber preferably through a heat exchanger where sensible heat is exchanged with the dilute working solution being con ⁇ veyed from the absorber to the desorber.
• Waste heat sources which have been used to power solution or absorption heat pumps, as described, can be obtained from either sensible heat, latent heat or both. Utilization of a sensible waste heat source has been maximized by extracting successive portions of heat for use first in the Rankine cycle evaporator section and then in the heat pump cycle desorber section of solution or absorption heat pump. Multiple cycle systems can also be employed to boost the temperature of a portion of the waste heat to even higher levels.
• Sources of this wasted heat include heat losses from boilers, drying equipment, chemical reactors, and fractionation equipment; low pressure steam which would otherwise be vented or condensed using air or cooling water and the like; and other low quality heat derived from a wide variety heat exchange equipment.
• substantial amounts of increasingly expensive fuel must be burned only to result in much of the heat produced being lost in a low grade form of waste heat. If a portion of this waste heat could be upgrade for further use, energy would be conserved and fuel cost savings realized.
• a temperature booster to be economically useful in a variety of industrial appli ⁇ cations where process steam is desired, should be able to exhibit a thermal efficiency of at least 40% per stage of temperature boost.
• a temperature booster In order to produce usable medium pressure process steam (i.e. up to 250 psig and 406°F.), a temperature booster should also be capable of providing a maximum temperature boost up to nine-tenths of the temperature difference between the waste heat and the low temperature heat sink used for waste heat rejection.
• the waste heat that drives a temperature booster machine is energy that is not hot enough to be useful with con- ventional technology. It is therefore an objective of the present invention to provide an absorption cycle heat pump booster system in a method which is capable of economically upgrading waste heat to useful levels and in particular, to provide a system and method for pro ⁇ ducing high quality, low to medium pressure process steam for a wide variety of applications using relatively low quality waste heat as the waste heat source.
• Waste heat at a temperature between about 180°F. (82 Q C.) and 300 q F. (149°C), such as from spent process steam or other sources, is fed into the evaporization zone of a first heat exchanger of an absorption heat pump apparatus where optionally the first heat exchanger in the evaporization zone utilizes the waste heat to vaporize a first fluid of a binary fluid at a relatively high pressure, the vaporized first fluid is then absorbed by the binary fluid in the absorber zone releasing both a heat of condensation and the heat of solution.
• a second heat exchanger in the absorber zone accepts the released heat from the binary fluid, thereby upgrading the temperature of the fluid, i.e. water, to produce low to medium pressure steam in the heat exchanger.
• the binary fluid after removal of some of its heat, as described, is then transferred to a second pressure vessel maintained at a pressure lower than the pressure of the evaporation and absorption zones of the first pressure vessel, wherein the first fluid of the binary fluid is vaporized by contact with another source of waste heat, preferably in the same temperature range as the temperature of the waste heat source for the evaporator.
• the resultant vapor is placed in contact with another, colder heat exchanger where it is condensed.
• the resultant condensate is transferred to the first heat exchanger for re-vaporation and the desorbed binary fluid is transferred to the first pressure vessel for further absorption of the first fluid vapor into the binary fluid after first evaporation.
• Another heat exchanger can be provided to exchange heat between the two binary streams flowing between the absorber and desorber.
• low quality heat in the form of 10 - 68 psia steam at 193 ⁇ F. to 300°F. (149°C.) to produce 20 - 250 psia saturated steam by the use, preferably, of a LiBr - Water binary system for the working fluid of the absorber and desorber described, where the concentration of the working solution as it enters the absorber is between 40% by weight of LiBr and 70% by weight LiBr and exits the absorber at between about 1% to about 10% less concentrated than initially and the concentration change of the working solution in the desorber is the same as in the absorber.
• the steam can be absorbed directly in the absorber section of the first pressure vessel and condensed in the desorber heat exchangers.
• This steam condensate can be used as feed water to a waste heat boiler, or utilized as feed water to the absorber heat exchanger and converted to process steam.
• absorption systems not only must efficient heat transfer occur in the absorber and desorber sections but also efficient mass transfer of refrigerant into and out of solution must occur.
• the desorber section of the system typically consisted of a chamber having heat exchange tubes immersed in a pool of binary solution.
• Heat transfer was limited by the surface area of the tubes, residence time of the solution, and back mixing, which occurred as new solution was fed into the chamber and as convective recirculation occurred in the pool. Mass transfer was similarly limited by what typically was the relatively small surface area of the pool of solution.
• heat exchanger apparatus com- prising vertical tubes with the waste heat source inside the vertical tubes and the concentrated LiBr-water work ⁇ ing fluid in heat exchanging contact with the outside of the tubes has exhibited inefficiencies in practice as previously described.
• a further objective of the invention is to provide an improved heat exchanger design and method for exchanging heat between a waste heat source and a binary working fluid preferably in an absorption heat pump unit and in particular the desorber section thereof.
• a refrigerant typically water
• the present invention provides improved heat exchanging contact between a source of waste heat and a binary working solution by providing a uniform film of binary working solution on the outside surfaces of a vertical tube heat exchanger.
• Fig. 1 is a schematic of one embodiment a solution heat pump system for producing low to medium pressure process steam according to the present invention.
• Fig. 2 is a schematic of another embodiment of solution heat pump, system for producing low to medium pressure process steam according to the present invention.
• Fig. 3 is . a schematic of a test apparatus for the evaluation of a vertical tube heat exchanger used as the desorber section of an absorption heat pump temperature boosting system.
• Fig. 4 is a cross-sectional view of the vertical tube heat exchanger of Fig. 3, taken along the lines and arrows 4-4 of Fig. 3.
• Fig. 5 is a partial broken cross-sectional view of one tube mounting embodiment of the present inventio .
• Fig. 6 is a partial broken cross-sectional view of another tube mounting embodiment of the present invention.
• Fig. 7 is -a partial broken cross-sectional view of still another tube mounting embodiment of the present invention.
• low temperature steam is introduced into a first heat exchanger 2 in - pressure vessel 10, through line 1.
• Heat exchanger 2_ heats a water fluid 3 in the first zone of pressure vessel 10 to produce water vapor which is absorbed in a second zone of pressure vessel 10, at 5 into a LiBr water binary fluid.
• the steam condensate from heat exchanger 2 passes through.a vapor-liquid separator trap 4 and is then passed to the condensate receiver 30.
• a portion of the steam that goes into line 1 is also directed via line 11 to the first zone of a pressure vessel 20 where it passes through heat exchanger 12 before being sent via line 14 through trap 17 to the condensate receiver 30.
• the heat exchanger 12 when heated by the steam, evaporates water from the binary working fluid passed over the heat exchanger 12.
• the water evaporated is condensed by heat exchanger 35 in a second zone of pressure vessel 20 and collects at 15.
• Concentrated binary solution at 13 is then transferred via line 16, preferably through a recuperative heat exchanger 18 and into the second zone or absorber zone of pressure vessel 10 where it is sprayed or otherwise placed in heat exchange relationship with heat exchanger 40 in the presence of the vapor from the first zone of the pressure vessel 10.
• the heat extracted by heat exchanger 40 is used to produce steam from the feed water.
• the condensate from the condensate receiver 30 can be used as feed water.
• the hot working fluid 5 from the pressure vessel 10 is further used in the recuperative heat exchanger 18 to heat the con ⁇ centrated binary fluid 13 before introduction into the absorber zone of pressure vessel 10.
• the steam generated in heat exchanger 40 is passed by line 41 into a steam drum 50 before eventual use. Cooling media is used in the heat exchanger 35 in the condenser zone of pressure vessel 20 to condense the water vapor at 15 desorbed from the binary fluid 13 by heat exchanger 12 in the desorber zone of pressure vessel 20.
• the condensed water 15 is transferred via line 22 into the evaporator zone of pressure vessel 10 to be evaporated by the low temperature steam passing through heat exchanger 2.
• An alternative configuration of this process could be equally effective if heat exchangers 2 and 40, and also heat exchangers 12 and 35, were in separate pressure vessels that were in vapor communi ⁇ cation between the respective pairs.
• the complete cycle described is capable of using low temperature steam of from about 180°F. (82 ⁇ C.) to about 300°F. (149°C.) and about 9 psia (62 kPa) to about 68 psia (469 kPa) to produce steam of from about 230°F. (110°C.) to about 400°F.
• a source of waste heat such as a fractionation tower 60 is used to heat a waste heat boiler 70 to produce low temperature vapor which is absorbed by a binary fluid in a pressure vessel 80 directly in contact with the absorber heat exchanger 75.
• the feed water for the waste heat boiler 70 is taken from the condenser zone of second pressure vessel 90, which is desorbed and condensed refrigerant . from pressure vessel 90.
• the binary working fluid and vaporized refrigerant are then introduced into pressure vessel 80 via line 74 and 71.
• the vaporized refrigerant is also introduced into the desorber zone of pressure vessel 90 vial line 72.
• the concentrated binary fluid 76 in pressure vessel 90 is transferred via line 74 through heat exchanger 78 to the absorber zone of pressure vessel 80.
• the dilute fluid 81 in pressure vessel 80 is cooled by the recuperative heat exchanger 78 before introduction via line 82 into the desorber zone of pressure vessel 90.
• the foregoing system description utilizing a waste heat powered boiler eliminates the need for a separate evaporator zone in the first pressure vessel 80.
• the pressure developed in the waste heat boiler can be from about 10 psia (69 kPa) to about 68 psia (469 kPa) at a temperature of about 193°F. (89°C.) to about 300°F. (149°C.)
• the refrigerant condensate 77 in the pressure vessel 90 which is then vaporized in 70, when added to the desorbed binary fluid 76 in the pressure vessel 80, will produce a binary working fluid 81 at a temperature of about 230°F. (110°C) to about 420°F. (215°C), having about 45% by weight LiBr to about 70% by weight LiBr in the pressure vessel 80 which will, when dsscrbed, produce a working fluid solution 76 containing 1% to 10% by weight less water than solution 81.
• the pressure maintained in pressure vessel 80 will equal the pressure of steam 71.
• the pressures maintained in the pressure vessel 90 will be less and should be between about 1 psia (7 kPa) to about 15 psia
• the typical sources of waste heat suitable for use with the present invention include: distillation and stripping towers or columns in oil refineries, chemical processing and the like; waste heat recovery from stack gases; blow heat recovery from pulp and paper processes; toasting and drying processes in the food industry; and exhaust gases from internal combustion engines and gas turbines.
• the system pressure, the heat transfer coeffi ⁇ cient of the tube and the range of heat transfer rates, the tube composition and surface condition and configuration, and the total surface area of the tubes, the length of the tubes and the manner in which the working fluid is held and initially introduced onto the surfaces of the tube, must all be considered when employing the concepts of the present invention in the design of an improved heat exchanger.
• the column apparatus shown in Figs. 3 and 4 was operated according to the parameters hereinafter _ described. Hot water to stimulate a waste heat source was introduced at 1' , Fig. 3, and conveyed into the interior of the vertical pipes 2' shown in Fig. 4. A fluid tight seal was provided at flange 3 1 to insure that the waste heat " containing water passed only vertically downward through the tubes 2' , shown in Fig. 4. A dilute solution, of typically LiBr and water from the absorber section of a solution heat pump, is introduced into the column 10' at 4 1 to contact only the outside of the tubes, shown in Fig. 3.
• Hot water to stimulate a waste heat source was introduced at 1' , Fig. 3, and conveyed into the interior of the vertical pipes 2' shown in Fig. 4.
• a fluid tight seal was provided at flange 3 1 to insure that the waste heat " containing water passed only vertically downward through the tubes 2' , shown in Fig. 4.
• Baffle plates 20', Fig. 5 are provided at several locations along the lengths of the column 10" and constructed in a manner to provide an open annulus through which the dilute LiBr-water solution will flow by gravity downwardly onto the surface of the tubes 2*.
• Centering device 28' is provided to maintain the relative position of tubes 2' and baffel plate 20'.
• the dilute solution will evaporate water as it picks up -waste heat from the water introduced at l 1 , into the intexior of the tubes 2 1 through the tube walls.
• the water vapor produced can be removed from the column 10' at various locations, such as points 11' and 12'.
• a condenser is provided to condense the water vapor to liquid water.
• the concentrated Li-Br-water solution reaching the bottom of the column 10 * is removed at 15', normally to be recirculated to the absorber section of a solution heat pump apparatus as described hereinbefore.
• the concentrated solution is removed at 15' and is introduced into a mixing tank 30' where it is diluted to the typical concentration of a dilute solution from the absorber section heat pump for reintroduction at 4' into the column 10' .
• the operation of the described exemplary apparatus has produced the following criteria for obtaining the results of the pre ⁇ sent invention.
• the main vertical section of the heat exchanger 10', outside of the tubes 2' is preferably maintained at a pressure of between 1 psia and 10 psia and more preferably between about 1 psia and 3 psia for best results.
• the temperature of the waste heat containing water is between about 180°F. (82°C.) and about 250°F. (121°C.) and preferably between about 200°F. (93°C.) and about 220°F. (104°C).
• the temperature difference between the waste heat source and the binary working fluid should be in the range of from about 5°F. (2.8°C) and about 25°F. (13.9°C), more preferably between about 10°F. (5.6°C.) and about 20°F. (11.1°C.) and most preferably less than about 15°F. (8.3°C.).
• the wide range of appli- cability of the present invention has been determined to be optimized by a flow rate of binary working fluid in the range of at least about 0,10 gallons per minute per inch of circumference and preferably from about 0.10 to about 0.40 gallons per minute per inch of circumference of the vertical tube used in order to achieve the improved efficiency of heat transfer of the present invention.
• a flow rate of binary working fluid in the range of at least about 0,10 gallons per minute per inch of circumference and preferably from about 0.10 to about 0.40 gallons per minute per inch of circumference of the vertical tube used in order to achieve the improved efficiency of heat transfer of the present invention.
• it is preferred to design the tube and baffle structure with the annular space 21' so as to distribute the binary working fluid as uniformly as possible onto the outer surface of the tubes within the flow rates previously described. - ;
• Several designs will function in this regard including . those shown in Figs.
• tubes 2' and distribution plates 20' are arranged with an annulus 21' and the plate 20' either provided with centering device 28', a porous pad 25* or a screen 26* .
• the centering device 25' will consist of rods of approximately the same dimension as the space between tubes 2' and installed in such a manner as to firmly hold tubes 2' in center of hole in distribution plate 20', thus forming a uniform annular space 21'.
• the pad 25' should be open enough in construction to permit sufficient free flow of the binary solution introduced above the distribution plate 20' through the pad 25' and the annulus 21' onto the tube 2' to achieve the identified flow rates.
• the pad 25' or screen 26* are forced into and partially through the annulus 21' to provide wicking and centering actions and better direct the fluid uniformly onto the outside surfaces of the tubes.
• An optimum design can be selected following the foregoing principles to achieve the functionality described without undue experimentation.
• additional design features can be utilized such as vertically splined tubes, and tubes with other special surface pre ⁇ paration including coatings and the like, if selected to minimize interference with the heat transfer from between the source of heat and the desired medium for receiving that heat and still promote uniform wetting of the exterior surface of the tube with binary working fluid. Any surface preparation or surface coatings should also be selected for their resistance to chemical attack by the binary fluid to minimize long-term maintenance problems in the design.
• the experimental desorber shown in Figs. 3 and 4 was designed as a -vertical shell and tube heat exchanger.
• the outer shell was fabricated from 8-inch schedule 40 pipe (carbon steel) with a tube sheet/flange at top and bottom.
• Twenty-one copper alloy tubes (0.75 inch OD) were used in this design.
• the total heat transfer length was 7 feet 10 inches.
• Two baffle plates or flow distribution plates were used to direct the flow of the dilute solution onto the tubes.
• One plate, such as shown as plate 20' in Fig. 5, was located 4 inches below the top tube sheet; the second plate was located 27 inches above the bottom tube sheet.
• the lower baffle was included to redirect any solution that may have splattered into the shell back to the tubes.
• a 1-inch drip ring was welded to the inside of the shell, 4 inches from the bottom tube sheet.
• the purpose of the desorber experiments was to measure the tube outside heat transfer coefficient (h ) Btu/hr ft 2°F * .
• the experimental runs were carried out for-the range of operating characteristics employed.
• the log mean temperature difference (LMTD) between the heating water and solution was calculated from measured temperatures according to:
• the tube outside heat transfer coefficient was calculated using the previously calculated value of U and the calculated value for the inside heat transfer coefficient
• the binary solution was observed to exhibit blowing or sputtering off the tubes due to the high heat transfer rate at low flow rates and vacuum outside of the range previously described.
• the vacuum is lower, more gas, such as nitrogen, is dissolved in solution, which tends to impede the desorption process.
• the effect of this is to reduce Q and LMTD, which seems to provide for adequate desorption to occur over the full tube length, which has the effect of raising h .
• the degree of vacuum affects h only in an indirect way.
• the low vacuum slowed down the total heat transfer by acting as an additional resistance in desorption of the vapor.
• the LMTD tests closely simulate the intended conditions for a desorber.
• the high h tests are the ones of greatest design interest.
• the vertical desorber described has a high heat transfer performance if operated under specific constraints identified.
• the present invention is then directed to a heat exchanger where the flow rate into a vertical tube heat exchanger, as described, is between 0.10 to about 0.40 gallons per minute per inch of tube circumference at a pressure for a desorber of about 19.5 in.Hg (5.2 psia or 35.8 kPa) and a temperature difference of less than about 15°F.

Landscapes

• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Mechanical Engineering (AREA)
• Thermal Sciences (AREA)
• General Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Combustion & Propulsion (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)
• Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)

Applications Claiming Priority (4)

Publications (1)

Family

ID=27099757

Family Applications (1)

Country Status (3)

Cited By (1)

Families Citing this family (5)

Family Cites Families (9)

• 1985
  • 1985-10-31 EP EP85905967A patent/EP0200782A1/de not_active Withdrawn
  • 1985-10-31 WO PCT/US1985/002160 patent/WO1986002714A1/en not_active Ceased
  • 1985-10-31 AU AU50982/85A patent/AU5098285A/en not_active Abandoned

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events