Novel cooling method for hot milk in India (photos)

Startup Promethean Power is developing a "thermal battery" that gets around unreliable power service in India at a clean-tech incubator in a converted warehouse in South Boston.


Martin LaMonica

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Thermal battery

Promethean Power has developed a novel energy storage system that uses a cold liquid to rapidly chill milk even when there's no power from the grid available. The company's first three cold storage systems will be deployed in India this year at processing centers. By having these types of systems, milk collection points can take milk from small farmers for longer hours, thereby giving them more opportunity to earn money. Seen here is a test system using water at Promethean Power's South Boston workspace at Greentown Labs, a clean-tech incubator. The warm milk, brought directly after milking, is poured over the cylinder-shaped tank and quickly brings milk to 4 degrees Celsius. See related story: A 'thermal battery' for villages in India.

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Cold Storage

Here is another view of the how milk would be poured over the cylinder-shaped tank to rapidly chill it. The tank is cooled from a liquid held in the thermal battery next to it. The thermal battery uses a combination of phase-change materials and other liquids that don't freeze until 27 degrees, lower than the freezing point. The chilling system can run on a car battery which allows milk collectors to process milk when the grid isn't working and avoid dirty diesel generators.

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Promethean Power co-founder Sam White (left) and engineer Ross Schultz stand in front of a prototype thermal battery. The cold liquid circulates from the battery behind them to the cylinder next to it to rapidly cool milk. The cold working fluid is then circulated to a traditional compressor to cool it again. By having this stored cold liquid, milk processors can chill milk even when the grid is not operating, avoiding diesel generators and allowing them to collect milk at more times.

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Milk jug

Sorin Grama (left) and Sam White hold the type of milk jug that's commonly used to collect milk from rural villagers in India. These jugs are loaded onto trucks or auto rickshaws to be brought to larger collection stations. Individual Indians may have only one or two cows.

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Rickshaw leaving

This still from a Promethean Power video shows a rickshaw filled with milk jugs about to go to a milk processing center where the milk will be chilled. The person on the right has brought his milk to the local collection point but did not make it in time and so will not be able to sell his milk. In its field tests, Promethean Power found that keeping collection stations open longer can increase the revenue of local farmers significantly. Often villagers travel long distances to bring milk to collection centers.

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Cold storage

The picture shows what a finished chiller and thermal storage system will look like. The compressor and thermal battery are packaged in the machine on the right and milk is poured into the container at the top of the stairs for storage.

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Pouring milk

Another Promethean Power image shows how milk, which is first put into collection jugs in villages, is then processed and chilled at larger collection stations.

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This photo shows a compressor, the type used in a refrigerator or air conditioner. In this prototype system, it's used to remove heat from the chilling liquid of the thermal battery and circulate it back in. As the printed "Mooo!" indicates, this system is designed specifically for chilling milk but the basic thermal battery technique can be used for other applications, particularly where there is not reliable grid service.

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Solar in Southie

Promethean Power originally envisioned building a milk chiller that ran with the aid of solar panels to create a less polluting system. After many trials and tests in the field, it found that the solar system was too expensive for India. However, the system can still operate in conjunction with solar panels. These are the panels they use for testing at Promethean Power's work space at clean tech incubator Greentown labs in South Boston.

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Cold storage, cold beer

The thermal battery concept is being tested by a local beer maker who wants to closely control the temperature of his brewing. The orange thermos is the thermal battery which stores the cold liquid and the tank on the right is fermenting beer.

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Greentown Labs

Promethean Power is one of the anchor tenants at clean-tech incubator Greentown Labs in South Boston, which has work space for engineers to build hardware prototypes and test them out. This photo is from their grand opening last year which attracted city officials and local entrepreneurs.

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