Super Optimize Carton Freezer
Fresh food packed in boxes to be placed on pallets by the producer and frozen by a freeze company by placing the pallets in a cartoon freezer that contains 40 to 50 tons each. The freezer is typically 15-20 m long and filled with pallets. The height is 2-3 pallets. The product is batch frozen. Evaporators and fans in the freezer ensures that the air circulation comes through on one side and back through the other.
This setup is far from optimal in respect to energy efficiency and short freezing time. To compensate for these problems, the air speed is increased and the air temperature is reduced. Substantial energy savings can be obtained by optimizing the airflow and thereby increase the evaporation temperature, which results in a higher efficiency of the refrigeration system.
The goal is to develop a freezer, where the direct energy consumption is reduced and the capacity is increased by optimizing:
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the packing of the pallets including new intermediate plates
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the air flow, pressure drop and temperature profile through the freezer
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the control system
The goals are obtained through models, laboratory testing, measurements and tests on an existing cartoon freezer. Both existing and new freezers are included.
Reduction in energy usage up to 30%.
A large amount of meat is frozen in batches in blast freezing tunnels. These tunnels are designed according to old rules of thumb, and they are in most cases running a constant air flow. By optimizing the running conditions of the tunnel, extensive energy savings can be obtained. In this report, a research project founded by Danish ELFORSK regarding the energy saving potential of industrial blast freezing tunnels verifies these savings potentials. The project covers testing of an industrial tunnel combined with laboratory tests, models and Computational Fluid Dynamics (CFD) simulations.
The main purpose of the project is to reduce the energy consumption by 30 %. The optimization of the fan speed, the air flow distribution through the tunnel and a new air spacer are investigated.
The project demonstrates that a considerable saving in energy can be obtained by adjusting the air flow and the air distribution in the freezer. By reducing the air flow, the pressure drop in the freezer drops, which results in reduced energy consumption.
The total time, in which the products stay in the tunnel, is determined by the logistics of the tunnel, i.e. when the unloading of the tunnel fits into the employees’ working schedule. Therefore, the energy optimization of the tunnel is about using the available time that the product stays in the tunnel in the most efficient way. The energy consumption of a test tunnel can be reduced by 86 % when reducing the air flow from 6.5 to 2.3 m3/s, and it is still possible to maintain the required final temperature of the product.
Similar tests in the industrial tunnel showed that by reducing the flow from 6.5 to 5.0 m3/s, the energy consumption was reduced by 61.9 %. The reason why the air flow was not reduced further was because the frequency drive was restricted and was running on lowest available frequency.
By introducing baffles to direct the flow to where it is needed, large energy savings can be achieved. By using baffles and reducing the flow to maintain the same freezing time as in the reference case, a saving in energy of 68 % can be expected. By reducing the air flow further down to 1.8 m3/s and still maintain the required final product temperature, the savings are estimated to be 93 %.
A new type of plastic air spacers was tested and compared to the wooden type which is normally used today. The results in the test tunnel showed a reduction in the freezing time of 4.9 hours and a slight increase in energy usage for the same adjustments of the fan as in the reference case. By reducing the air flow to 2.8 m3/s, a saving of 78.6 % was obtained. The freezing time was 30.7 hours, and therefore there is room for more savings by reducing the air flow further.
The conclusions are based on 25 different tests. 18 tests are performed in a test environment at Danish Technological Institute, and the last seven tests are performed in an industrial blast freezing tunnel at Claus Sørensen A/S; a big tunnel freezing company in Denmark with a number of tunnel freezing plants.
Key figures
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Participants
| Partner | Subsidy | Auto financing |
|---|---|---|
| Claus Sørensen A/S | ||
| Hørup Maskiner | ||
| Güntner GmbH & Co. KG |
