Upper Styrian Dairy (Austria)

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Obersteirische Molkerei Knittelfeld (Austria)

(Upper-Styrian dairy in Knittelfeld)

1. Solar integration

A solar plant has not yet been built. The first step was, to examine possible strategies for energy efficiency and to evaluate the application of solar technology for supplying process-heat in terms regarding technology and economics.

2. Industry Sector


3. Industrial application

Process-water heating and integration in a central warm-water store

4. Process description

  • Process flowsheet:

Process description-Upper Styrian Dairy (Austria).jpg

Fig: Flowsheet of the “Upper-Styrian dairy in Knittelfeld”

  • Processes:

Processes with thermal energy demand

Processes with thermal energy demand-Upper Styrian Dairy.jpg

5. Energy flows and temperature ranges
  • Main heat supply system and fuel:
Gas consumption: 228,3 Nm³/month
339,57 Nm³/h
Gas consumption for the processes: 2.771.514 Nm³/month
Gas consumption for heating: 196.644 Nm³/month
  • Energy consumption (Sankey):

Energy consumption (Sankey).jpg

Fig: Energy-balance of the dairy

  • Temperature ranges and other parameters:

The steam energy which is produced in the boiler, is needed for whey-concentration (38%, 9.100 MWh/a), for heating the boiler-feed water up to 102°C (11%, 2.700 kWh) and for the remaining thermal processes (29%, 6.900 MWh/a), whereof the milk-cheese pre-heating and the heating prior to the whey-concentration are the biggest energy consumers. The reflux-condensate contains 2,5 % of the energy. Heating consumes 8% of the total energy (1.900 MWh/a). 25 % (!) of the energy (5.900 MWh/a) cannot be clearly related to any process. Of this value, the basic demand requires 4.800 MWh/a and 1.100 MWh/a have to be used for balance-adjustment in the process.

6. Solar Thermal Plant

6.1 Solar process-water heating

6.1.1 Process scheme and description

Solar Thermal Plant.jpg

In total, 65 m³/day of process-water (fresh-water) at 65 °C are needed in the milk- and the cheese-dairy. The fresh water has a temperature of 12°C. Because there is no continuous process-water demand, a storage-tank is necessary, but the hot water can be taken directly from the store. The heat-storage-medium is heated in the collector and heats the fresh-water, which is then gathered in the store, via a simple heat-exchanger.

There is only one heat-exchanger necessary to integrate the solar system, therefore the heat-transfer losses sink and the efficiency of the solar energy rises. The final temperature of the water after the solar system was defined as 55°C. The heating up to 65 °C is done via after-heating. Two solar plants with different solar ratios were simulated.

6.1.2 Performance of the planned solar plant

Performance of the planned solar plant.jpg

Over the whole year, an energy input of 470 MWh/a with 1000 m² collector area and 584 MWh/a with 1500 m² area can be achieved.

6.2 Integration of the solar system in a central warm-water store

6.2.1 Process scheme and description

Integration of the solar system in a central warm-water store.jpg

In this option, the process water shall be heated up to the required temperature of 65°C only by means of the solar system. In this case, the integration of the solar plant into a holistic storage-system would make sense. In the dairy, there are also the boiler-feed water and the “Bruchwaschwasser” (break-washing-water?), which can both be pre-heated to 45°C via heat exchangers with final temperatures of 102 and 65°C. By the integration of solar heat into a central store, all three streams “process-water”, “boiler-feed water” and “Bruchwaschwasser” can be heated. The practical application could be done with a single big “Schichtspeicher” (store), into which the waste-heat for the heat exchangers at 38 and 50°C and the solar energy at higher temperatures can be inserted.

6.2.2 Performance of the planned solar plant

Performance of the planned solar plant1.jpg

The decline of the specific collector-output is clearly visible. Thus the economics of the collector area also decrease. Based on the present state of knowledge, the direct solar process-water heating is preferable to the integration in a central store!

  • Pictures of the built solar system:

No information available.

7. Energy savings
  • Pinch analysis results:

Calculated heat-exchanger network:

Calculated heat-exchanger network.jpg

The following thermal energy demand has to be supplied additionally:

Calculated heat-exchanger network2.jpg

  • Energy savings:

Energy savings with option A (1000 m²): 469.600 kWh/a Cost savings option A: 20.780 €/a

Energy savings with option B (1500 m²): 583.100 kWh/a Cost savings option B: 25.802 €/a

8. Economic evaluation
  • Economic parameters of the built solar system:

Solar process-water heating:

Solar process-water heating2.jpg



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