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Content archived on 2022-12-27

INTEGRATION OF PROCESS MODIFICATIONS WITH ADVANCED ENERGY SYSTEM AND SERVICES IN DAIRY PROCESSING

Objective

This project demonstrates the potential for energy savings in a modern dairy plant. The plant has high seasonal variations in production, with end products of high value and quality.
The aim of the project was to reduce overall energy costs by process integration, incorporating an advanced energy control system for the milk handling, storage and processing plant.
The initial objective was to reduce overall energy costs by 10%, by a combination of energy saving, and by transferring electricity demand to the "off-peak" cheaper rate tariff.
In terms of energy saving, the project has been a total success and although the expected transfer of energy demand to the off-peak tariff was not completely achieved, the project fully demonstrates the potential for significant and cost-effective energy savings in dairy processing. The 4% reduction in electricity use contributes to a reduction of 450 t (Carbon equivalent) in CO2 emissions associated with electricity generation.
The results achieved by Golden Vale have been very encouraging. In terms of energy saving the project has been a total success. In fact, the energy savings are expected to increase over the life of the project.
Most of the problems that arose during the commissioning and trials period were of a minor nature. The experience gained in solving these problems will be useful for any future similar projects. Some problems arose which were related to individual components of the refrigeration plant. Software difficulties did lead to a time overrun. However, the cost overrun was small, amounting to less than 2,5%.
This project, to exploit the potential for energy and cost savings in a milk processing plant, subject to fluctuating seasonal variations, was carried out at Golden Vale plc.
Heating and cooling are essential requirements in all dairies. Typically, all incoming milk is cooled to 4 deg. C, prior to separation. This is carried out in order to store the milk and match the supply to the separation process. During the separation process, the milk is heated to 60 deg. C. The skim is then recooled to 4 deg. C for further storage, before passing to the evaporation and drying plants. Golden Vale's plant operated in this way, which is typical of many such plants. These plants are not designed to optimise on the energy saving benefits of processing unchilled milk. This results in high energy costs associated with chilling, heating and subsequent rechilling. Golden Vale's energy sources are a combination of natural gas and electricity. As the peak demand for processing coincides with the moreexpensive electricity tariff, significant savings were possible by converting to the cheaper, off-peak tariffs. Additional savings were possible if energy use could be controlled in order to minimise maximum demand charges.
To exploit the energy saving opportunities identified in its studies, Golden Vale :
- Developed a fully integrated system to manage peak demands for energy in purge/wash cycles. Depending on stock levels of unprocessed milk, on the time of day, and on plant availability, up to 30% of milk throughput can be sent immediately unchilled through separation and on to the powder plant evaporators.
- Installed a cold "cold accumulator" to reduce the daily requirements of the chilled water system by up to 50%. The two storage units, each of 4 MW capacity, operate on cheap night-rate electricity, and utilise three of the existing refrigerant compressors and one evaporative condenser.
- Introduced a system to control the remaining 20% of cooling to minimise maximum demand charges. When the site cooling demand is low, the cold accumulator is topped up by running the compressors and cooling in the hydro-cooler mode. At high cooling demands, the cold accumulator is brought into discharge mode. Alternatively, part of the milk is processed unchilled, or a combination of by-pass and chilling is used.
- Installed product flow monitors to reduce energy consumption during purge/wash cycles, and isolation valves to eliminate steam pipeline "dead legs" and reduce thermal radiation losses.

Call for proposal

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Coordinator

GOLDEN VALE FOOD PRODUCTS LTD
EU contribution
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Address
CHARLEVILLE
COUNTY Cork
Ireland

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Total cost
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