USE OF SURPLUS HEAT FOR DRYING OF MACROALGAE

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1 USE OF SURPLUS HEAT FOR DRYING OF MACROALGAE Tom Ståle Nordtvedt Senior Scientist

2 Agenda Surplus heat from industry WP 5 Objectives Tafjord plant Drying tests Results 2

3 Offshore heat supply on electrification Statoil Sverdrup Metals processing Sketch Statoil Foodstuffs REMA 1000 / Danfoss / Fish processing Industrial Symbiosis Mo Industripark 3

4 WP 5: Focus and objective WP5 will focus on the application of surplus heat in processing of macroalgae. Frame conditions for analyses and the model development will be highly influenced by the industries represented in the project consortium. The industry partners will further provide cases where resulting concepts from the project will be tested, ensuring industrial relevance. The estimation of economic and environmental gains will be performed through collaboration with WP6. 4

5 Tafjord plant

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7 Sources of energy at the Waste to Energy plant # Medium Temp. C Pressure, bar Flow, t/h Max. Output 1 HP Superheated Steam, ,5 turbine mainline 2 LP Saturated Steam from deaerator 3 Hot water, district heat line Salt Water from scrubber ,1 4,5 0,9 cooling and moisture condensing 5 Air heating from flue gas cooling MW Moisture removal kg/s In a short term, # 3, hot water from the district heating line, is the most likely to use in the harvesting season, i.e. the summer. Other sources, may be utilized when needed, especially for secondary processing on an all year basis. # 4 and # 5 will be energy recovered.

8 Primary processing capacity 1000 kg of seaweed requires removal of 720 kg moisture, corresponding to kj or 1000 kwh, or 1 MWh. Hence 1 MW corresponds to 1 t/h of seaweed primary processing. 50% of the district heating capacity in the harvesting season 10 MW, corresponds to primary processing of resp. 10 t/h 240 t/d or 7200 t/mth. Secondary processing capacity Assuming a finished product with less than 10 % moisture content, requires removal of 40 minus 11 percent moisture, dry basis. To dry the initial 1000 kg of seaweed into a finished product, further 60 kg of moisture must be removed, corresponding to kj, or 83,3 kwh. Hence, the energy required for the secondary processing is significantly less then for the primary processing.

9 Available energy in the district heating system Climatic Heating Profile Ålesund 2015 jan feb mar apr mai jun jul aug sep okt nov des The harvesting season coincides with the low season for heating in Ålesund. Therefore, energy is available for primary processing of seaweed. One may assume that 50 percent, or 10 MW, is available in that season.

10 Pre-treatment of seaweed (1): Due to short harvesting period and short shelf-life on fresh raw material, there is a necessity for a pretreatment for better conservation. 1) Chemically (formaldehyde/acid) not for human consumption 2) Partially dried Tested 3) Freezing Industrially freezing/thawing for storage and further processing. Tested in RFF project ISBIT 1 and ". 10

11 Sorption isotherm, and the importance of the water activity (aw) Stability of the product is directly related to aw. Will influence on microbial growth, enzymatic reactions, oxidation etc. Equalization of water content (and aw) in product related to relative humidity (% RH) in surrounding air. Define necessary water content and air humidity for stability during storage For dried products, the sorption isotherm defines necessary final water content of the product. Defines necessary relative humidity of the drying air to reach final water content. Important for designing the drying equipment and the thermal capacity of the thermal system.

12 Drying of seaweed : Challenges: - Different temperatures => different technologies - Stickiness - Monolayer drying - Short shelf-life 12

13 Air drying metodes Theoretically, a lot of different drying equipment may be used for dehydration of seaweed. Based on the task of utilising surplus heat and/or steam, indirect dryers and steam dryers will be most suited for further discussion. Hot air driers Conveyor (belt) dryers. Bin and cabinet dryers Tunnel driers. A rotary dryer A fluidised bed dryer Contact driers Drum dryers The rotary disc dryer The indirect tube dryer 13

14 Drying of larger amount of Sugar kelp Figure 12: Over 100 kg of frozen Sugar kelp was thawed at +4C, and dried at 70 C for 2 hours before it was finally dried at 30C.

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16 Sugar kelp

17 Drying challenges Figure 8: The thickness of different leafs variates, which leads to a certain uneven drying rate. The Sugar kelp turns green when it is dried.

18 WP5: Results Suitable dewatering and drying equipment with use of surplus heat from the industry, will be able to produce stable seaweed products. Optimal drying temperature and humidity essential for producing high quality products for human consumption. Tafjord Kraftvarme, Foto: Sunnmørsposten Environmental friendly and energy efficient production by use of correct equipment ensures viable processes. Drying equipment, Foto: SINTEF Foto: SINTEF 18

19 Teknologi for et bedre samfunn