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PUMPABLE ICE TECHNOLOGY

Terminology

Pumpable Ice, Technology (PIT) is a technology the main goal of which is to produce cooling medium (Pumpable Ice - PI), also known as “coolant” (do not confuse with “refrigerant”), with a viscosity of water or jelly and the cooling capacity (a potential to cool) of “ice”. The PI consists of the water based liquid with any crystallization temperature, ice crystals ranging from 5 microns to 1 cm (10,000 “micron”) and gas bubbles (e.g., air, ozone, CO2).

History

The first time, the possibility to mix water with ice and to pump this PI was realized by US Company called this mixture “liquid ice”.

In the most cases, a fresh water solid ice, such as flake ice, plate ice, tube ice, shell ice or cubic ice, is crushed or grinded, mixed with a sea water or salted water and pumped by conventional water pumps.

Besides general terms such as “pumpable”, “jelly”, “slurry” ice, there are many other trademarks for this coolant such as “Beluga”, “optim”, “fluid”, “jel” “binary”, “liquid”, “maxim”, “whipped”, “deep chill”, “bubble slurry” ice. These trademarks are authorized by industrial ice maker production companies in Canada, China , Germany, Iceland , Israel , Russia , Spain , United Kingdom , USA.

Technological process

There are two relatively simple methods for the production of PI.

The first is to manufacture commonly used forms of crystal solid ice such as plate, tube, shell or flake ice, by crushing and mixing it with water. This mixture of different ice concentrations and dimensions (ice crystals can vary from 200 micron to 10 mm) is passed by pumps from storage tank to the consumer. The constructions, specifications and applications of the current regular ice makers are described in.

The idea of the second method is to create the crystallization process inside of the volume of the cooled liquid.

Crystallization inside of the liquid’s volume can be accomplished by the vacuuming or cooling technology. The vacuum technology is based on solid-liquid-vapor multiple phase transformation. An ice is created in a vacuum tank by flashing water vapor and by forming ice crystals at the same time. Depending on the additives’ concentration, the final temperature of PI is between 0ºC and minus 4ºC. The large volume of vapor and an operating pressure of about 6 mbar require the usage of a water vapor compressor with a large swept capacity.

This PIT is economically reasonable and can be recommended for systems with cooling capacity of 300 TR (1 TR = 1 ton of refrigeration = 12,000 BTU/h = 3.516 kW) or larger.

Crystallization by cooling can be done using the direct or indirect systems.

The direct PITs

A refrigerant is directly injected inside the liquid

The advantage of this method is the absence of any intermediate device between the refrigerant (R) and the liquid (L). However, the absence of heat loss between R and L in the process of thermal interaction (heat transfer) may cause some insufficiencies that could keep this method from its wide inoculation into the industry. The high level of safety measures and difficulties in producing crystals are disadvantages of this method.

Indirect PITs

In the indirect PITs the evaporator (heat exchanger-crystallizer) is assembled either horizontally or vertically. It have shell tubing assembled with one to a hundred inner tubes and containing a refrigerant that evaporates between the shell and the inner tubing. A liquid flows through the tubing of the small diameter.

The idea is to use a well-polished surface of the evaporator and appropriate mechanisms to prevent tubing from the adhesion of ice embryos, from a growth and a thickening of the ice on the inside cooling surface. A whip rod, a screw or a shaft with metallic or plastic wipers is usually used as mechanisms for removal.

Indirect PITs produce pumpable ice (PI) consisting of 5 to 50 microns crystals and having a number of advantages, such as low energy expenditure of ice production (70 kWh per 1,000 kg pure ice), a high specific ice capacity per an area value of the evaporator cooling surface (up to 450 kg/m²/h)) and utilization of conventional water pipes and pumps.

Sometimes a gas can be added to the liquid flowing through the evaporator. It destroys a liquid laminar layer on the cooled surface of the heat exchanger-crystallizer, increases flow turbulence, and decreases the average viscosity of PI.

Liquids, such as sea-water, juice, brines, or glycol solutions of additives with more than (3 ÷ 5)% concentrations and a freezing point less than minus 2ºC are used in the process.

The PI with maximum ice concentration of 40% can be pumped straight from the ice maker to the consumer. The final possible ice concentration of PI in the storage tank is 50%. The maximum value of cooling energy of PI, accumulated in the storage tank in a form of homogeneous phase, is about 700 kWh which corresponds to (10 ÷ 15) m³ volume of a storage tank. A mixer is used to prevent a separation of ice from the cooled liquid and keeps an ice concentration unchanged by time and the tank height. In this case the PI is transported from the storage tank to the place of consumption that could be hundreds meters apart. The practical ratio between the required electrical power of the mixer motor (kW) and the “kneaded” PI volume (m³) is 1:1.

In the tanks with volumes larger than 15 m³, PI is not mixed and the cold energy of stored ice is only used by a heat transfer of liquid that circulates between a storage tank and the consumers of cold.

Applications

Typically, the equipment for the production, accumulation and supplying of PI includes an ice maker, a storage tank(s), a heat exchanger, a piping, pumps, electrical and electronic appliances and devices.

This equipment can be used in the cooling processes in the chemical, fishery and food industries, , in the centralized air conditioning systems, in the thermal energy storage systems (TESS) , for air cooling in the supermarkets’ counters (showcases) , for the production of special wines (reminiscent of similar "Richwine" or "Ice wine").

PIT can be recommended for the processes of concentration of juice, concentration of wine with low alcohol content, cleaning (lightening) of waste water and desalination of sea (salt) water.

References