Classifications

• • 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
  • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
  • F25D31/00—Other cooling or freezing apparatus
• • 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
  • F25C—PRODUCING, WORKING OR HANDLING ICE
  • F25C2301/00—Special arrangements or features for producing ice
  • F25C2301/002—Producing ice slurries

Definitions

• This invention relates to a method of generating of ice slurry.
• this invention relates to method of generating of ice slurry under vacuum conditions.
• Ice slurry is a suspension of water based ice crystals in a solution of either pure water or water containing additives like freezing point depressants.
• Ice contained in the ice slurry makes it very effective for preserving the cold. Ice slurry can be pumped to consumption points easily. It has potential use as a secondary cooling medium, either by direct application on the product or alternatively as a thermal energy storage media, whilst remaining fluid enough to pump. Ice slurry offers superior performance over the conventional flake and block ice systems as a chilling medium. Ice slurry offers higher efficiency and cost effective ice production and also unique pumping and easy handling characteristics.
• Ice slurry is called by brand names of "Liquid-ICE” or “Pumpable-ICE” or “Binary Ice” or “Flo Ice” or “Vacuum Ice”.
• Ice slurry systems provide totally sealed "Hygienic Systems" for applications in fisheries, supermarkets etc., enhancing productivity, flexibility of operating temperature and consistency of application. To remain pump-able only a portion of the water (5 to 30%) should be transformed into small ice crystals of size around 1 mm., but not more. This ensures a uniform solution while enhancing cold transfer.
• Another known method producing ice slurry is under vacuum utilizing triple point conditions of water.
• the triple point of a substance is the temperature and pressure at which three phases (gas, liquid, and solid) of that substance may coexist in thermodynamic equilibrium.
• the vacuum is created by using water vapor compressors.
• the system utilizes electricity as energy source.
• thermo compressors use thermal energy in the form of steam as energy source.
• the thermo compressors are generally low efficiency devices which require much larger quantity of steam to produce unit refrigeration effect.
• US patent 4,734,116 discloses a method and apparatus for generating ice slurry with ethanol as an additive, producing vacuum by sucking water vapors using a compressor #nd compressing a flow of water vapor to a condensation chamber in which the compressed water vapor is condensed.
• Ice slurry generators employ mechanical refrigeration for slurry production. Ice crystals are generated on refrigerated surface over which water along with freezing point depressants is flowing. Ice crystals are then scraped off mechanically from the surface to form slurry with water.
• thermo compressors resulting in very high steam consumption figures.
• the surface temperatures are of the order of -10 to -15°C leading to higher electrical power consumption.
• Yet another limitation of mechanical systems is that there is a much higher requirement of freezing point depressants since ice is produced at much lower temperatures.
• An object of this invention is to provide a method and apparatus for generation of ice slurry which is efficient and consumes considerably less energy to produce unit refrigeration effect.
• Another object of this invention is to provide a method and apparatus for generation of ice slurry which is compact in size and at the same time consumes much less electrical energy.
• Still another object of the invention is to provide a method and apparatus for generation of ice slurry which requires comparatively less amount or even no freezing point depressants.
• One more object of the invention is to provide a method and apparatus for generation of ice slurry which is economical and in which the method can be precisely controlled.
• Yet another object of this invention is to produce ice slurry in a slurry generator under stable and homogeneous conditions.
• vacuum is created in the ice slurry generating chamber by permitting communication between the absorber unit of a lithium bromide vapour absorption machine and the said chamber.
• ice slurry is re- circulated in said chamber until desired concentration of ice in the ice slurry is achieved.
• a Lithium bromide vapour absorption machine comprising an absorber unit having : cooling tubes; means for spraying concentrated lithium bromide solution on said tubes; a shell in communication with said chamber to permit contact with vapour in said chamber with the lithium bromide solution and absorbing said vapour in said unit for creating vacuum in said chamber; means for collecting dilute lithium bromide solution with water vapour absorbed from said unit and pumping said dilute lithium bromide solution to a high temperature generator unit to regenerate concentrated lithium bromide solution and water.
• the said chamber is located operatively directly below said absorber unit.
• said chamber is located operatively below and towards one side of the absorber unit.
• the absorber unit has a single set of cooling tubes and a trough is provided below said column for collecting and removing dilute lithium bromide solution with absorbed vapour.
• the absorber has at least two sets of cooling tubes and troughs are provided operatively below each set for collecting and removing dilute lithium bromide solution with absorbed vapour.
• the chamber is provided with a defrosting mechanism.
• Figure 1 shows a schematic sectional view of the Ice slurry generator configured to produce ice slurry as per this invention
• FIG 2 is the schematic diagram of an alternative embodiment of the Ice slurry generator of Figure 1;
• Figure 3 is one more alternative embodiment of the generator of figure 1.
• the weak solution from an Absorber is pumped by a solution pump to a high temperature generator (HTG) via a low temperature heat exchanger and a high temperature heat exchanger.
• HOG high temperature generator
• Heat is added from a heat source like steam to the weak LiBr solution in this generator and the refrigerant which is typically water is evaporated.
• the high temperature heat source is generally at a temperature higher than 14O 0 C. This step concentrates the LiBr solution to make it stronger.
• the stronger LiBr solution flows to a low temperature generator(LTG) via the shell side of the high temperature heat exchanger.
• the refrigerant generated in the high temperature generator is then condensed on the tube side of LTG, thereby providing more heat to the solution arriving from the HTG. More amount of refrigerant is generated in LTG . The stronger solution from the LTG is then passed back to the absorber via the shell side ofthe LTHE to complete the cycle.
• vapour absorption machines produce refrigeration effect only at temperatures above the freezing point of water.
• the liquid refrigerant water freezes in an uncontrolled manner and forms lumps of ice over the evaporator tubes or refrigerant storage below it. In fact it becomes hindrance to the operation and there is possibility that chilled water inside the tubes may also freeze. The machine fails to perform further under such conditions.
• This invention proposes a method to produce ice slurry using Vacuum absorption cycle and lithium bromide as an absorbent with water as the refrigerant.
• This invention also proposes a method to produce ice slurry in a slurry generator using a modified LiBr VAM configured to operate at temperatures close to freezing point of water.
• the ice slurry generator 100 configured to produce ice slurry as per this invention is generally indicated by reference numeral 100.
• the ice slurry generator 100 comprises an evaporator chamber (1) which is provided with an agitator (2). and is subject to vacuum conditions of a vapour absorption machine.
• the chamber 1 is preferably provided with a defrosting mechanism (3) which has provisions for controlled circulation of heating water.
• An ice slurry pump (4) is provided to pump out the ice slurry from the chamber 1 to the desired application point.
• a return pipe (14) is provided through which dilute ice slurry or make up refrigerant is returned to the chamber 1.
• the pump 4 is adapted to return the ice slurry solution to the chamber until the ice slurry is of suitable concentration for the particular application.
• the chamber 1 is in communication with the absorber unit 5 of a Lithium Bromide vapour absorption machine.
• the machine has an Absorber(5) a Condenser (6) Low Temperature Generator (LTG) 7, High Temperature Generator (HTG) 8, Low Temperature Solution Heat Exchanger (LTHE) 9, High Temperature Solution Heat Exchanger( HTHE ) 10, Heat Reclaimer (HR) 11, Interconnecting Piping, 12 Solution Pump 13 all common as in any conventional LiBr VAM.
• the weak solution from Absorber (5) is pumped by solution pump (13 ) to (8) [HTG] via LTEE (9) and HTHE (10).
• Heat is added from a high temperature heat source like steam to the LiBr solution in this generator and refrigerant is evaporated.
• the high temperature heat source is generally at a temperature higher than 140 0 C can be any thing like high temperature pressurized hot water, steam, direct firing of oil / gas or waste heat from any exhaust gases such as DG sets.
• the stronger LiBr solution flows to (7) [LTG] via shell side of high temperature heat exchanger (10).
• the refrigerant generated in HTG is then condensed on the tube side of LTG, thereby providing more heat to the solution arrived from HTG. More amount of refrigerant is generated in LTG (7).
• the strong LiBr solution from LTG (7) is then passed back to absorber (5) via shell side of the LTHE (9) to complete the cycle.
• the typical temperature of the strong LiBr solution is around 45 degrees Celsius.
• the refrigerant vapor generated in LTG (7) is condensed in the condenser (6).
• This liquid refrigerant [water] is then passed to the ice slurry generator (1) to complete the refrigerant cycle.
• the liquid refrigerant can also be taken out of the system and replenished with the new refrigerant.
• the defrosting mechanism 3 By use of the defrosting mechanism 3 the formation of ice in the ice slurry generator chamber (1) is controlled.
• the defrosting mechanism allows relatively hot water around 30 degrees Celsius to jacket the outer wall of the chamber 1. This hot water jacket prevents icing of the walls of the chamber 1 and is used intermittently as a defrosting unit.
• the chamber 1 is in communication with the absorber unit 5 .
• the absorber unit 5 has cooling tube sets where cold water again at temperatures around 30 degrees Celsius is circulated through sets of tubes. There may be one central set 15 as seen in figure 1 or two sets 16 and 17 as seen in figure 2. More than two sets of tubes may also be fitted in the absorber 5. Concentrated strong Lithium bromide solution from the LTG 7 unit of the machine is sprayed by sprayers 18 on the tube sets 15,16 and 17.
• the tube sets are provided with cooling water inlet 19 and cooling water outlet 20.
• the concentrated lithium bromide solution absorbs vapour in the absorber from the chamber 1.
• the weak lithium bromide solution is collected in the trough/troughs 21 and led off through conduit/conduits 22 to the pump 13
• This absorption performs two functions: it generates heat, because the absoption of vapour in the LiBr is an exothermic reaction which is taken up by the cooling tube sets and 2 it reduces the pressure in the absorber chamber .space causing more water present in the chamber to evaporate.
• the heat for this evaporation is taken from the resident water/dilute ice slurry solution in the chamber 1 thereby cooling the water.
• ice crystals are formed in the ice slurry generator.
• agitator (2) rotating at a range of 400 to 1500 revolutions per minute and typically 600 rpm , ice crystals are mixed thoroughly with the solution present in the ice slurry generator and thus ice slurry is formed.
• Slurry pump(4) is used to take away slurry, once it has reached the desired concentration.
• the diluted ice slurry or make up refrigerant is returned to the ice slurry generator via pipe (14). Part of the ice slurry is re circulated back to the slurry generator for maintaining stable operation and consistency of ice slurry.
• the evaporator/ice slurry generator chamber 1 is located operatively directly below the absorber unit 5 of the vapour absorption machine and the shell of the absorber and the that of the chamber 1 are continuous whereas in figure 3 the absorber 5 opens on one side and the chamber is positioned on one side of the absorber affording a more compact design.
• An ice slurry generator with LiBr Vapor Absorption Machine was built to deliver 35 Tonnes of refrigeration capacity (Approx. 25000 kg/ per day) of fresh ice generation.
• the machine was operated with steam at 8 kg/cm2 pressure as heat source. Cooling water at 32°C was used as heat sink in the absorber tubes. It was observed that as the pressure in the absorber reached below triple point of water small ice crystals formed in the solution which was in the ice slurry generator. Different types of inorganic salts were used in small proportions as freezing point depressants.
• the machine delivered ice slurry with ice percentage between 2% to 15%.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
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• Physics & Mathematics (AREA)
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• Thermal Sciences (AREA)
• General Engineering & Computer Science (AREA)
• Sorption Type Refrigeration Machines (AREA)

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• 2007
  • 2007-08-31 EP EP07866694A patent/EP2061999A4/de not_active Withdrawn
  • 2007-08-31 WO PCT/IN2007/000390 patent/WO2008062438A2/en active Application Filing

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