Introduction
Drying typically accounts for more than 60% of the energy demand in aquafeed extrusion, and for most facilities this energy still comes from fossil fuels. As feed mills face pressure to improve sustainability and emissions in aquaculture and prepare for possible carbon regulations, aquatic feed dryers become a natural starting point for decarbonization efforts.
Past attempts at heat recovery have been limited by two persistent challenges: (A) exhaust air is hot, humid, and dust‑laden, causing fouling and performance decline in heat exchangers; and (B) conventional energy sinks, mainly dryer make‑up air, represent only 10–15% of the dryer's thermal load due to the main load deployed onto recirculated air inside dryers. To unlock larger savings, both of these source and -sink side challenges must be addressed.
This paper presents a modular approach enabling aquafeed producers to increase heat recovery today while preparing for hybrid or fully electrified dryer operation in the future.
Modular Heat Recovery Pathways and Exhaust Air Pre-Treatment
The challenges of dust-laden air, fouling and lack of heat sinks must be addressed for successful decarbonization of aquatic feed and improving sustainability in aquaculture in general. A dedicated Heat Recovery Unit (HRU) is introduced here. The HRU combines exhaust air cleaning and coil area into a single modular system that can be expanded over time. At the HRU inlet, a rotating drum‑filter with suction nozzles removes fine particles from the wet exhaust stream. This step prevents fouling of the heat exchanger coils, stabilizes heat transfer performance, and maintains consistent back pressure towards the dryer. Once the air is cleaned, the HRU can transfer energy into one or more sinks depending on the different integration pathways:
Preheating dryers make‑up air or process water. This provides a straightforward energy efficiency improvement and typically recovers 10-15 % of dryer energy.
Preheating process water for the feed manufacturing process, including boiler feedwater
Building- and facility heating,
Auxiliary water heating, e.g. cleaning water.
With suitable HRU sizing, integration with high-temperature heat pumps to get to temperatures that allows heating of air internal to the dryer. This hybrid approach enables substantial reductions in fossil fuel, and supports future electrification using natural refrigerants
Because the HRU is modular, aquafeed producers can adopt the level of integration that matches their site's energy demands and investment horizon, starting with basic heat recovery and progressing toward partial or full electrification when conditions are favorable.
Performance Outcomes and Decarbonization Potential
The integrated filtration and HRU system significantly increase the recoverable portion of dryer energy, with 28-53% recovery depending on coil configuration. When combined with a high‑temperature heat pump using a natural refrigerant, the system can cut energy use by up to 64% and operate with up to 100% electric heat input, offering a practical pathway toward decarbonization of feed for aquaculture.
In parallel, fine‑particle removal (F7 ≈ 65% of particles below 2.5 µm) improves air cleanliness and reduces odor, which can be valuable for aquaculture feed plants located near communities or sensitive environments. Water condensation from the exhaust stream also yields 350–900 kg/h of recoverable water, depending on configuration.
Economic modeling shows a solid commercial foundation for HRU‑only systems (1-2 years) and medium term and tangible ROIs for hybrid dryer heat pump integration, depending on regional energy prices. The overall pathway enables both immediate savings and long-term readiness for high‑efficiency, low‑carbon aquafeed production.
Performances for energy recouperation and decarbonization aspects of the different integration levels / solutions is seen in Table 1.
Table 1. Example numbers for HRU systems as well as for its integration with the hybrid dryer using high-temperature heat pumps using natural refrigerants.
| Dryer @ 1.6 MW 10 tons/h feed | 2.1 tons H2O/h |
Heat recuperation (HRU) | Hybrid dryer integration | |
|---|---|---|---|
| 1 coil bank | 2 coil banks | 2 coil banks | |
| Particle fines removal | F7 | F7 | F7 |
| Odor reduction | + | ++ | +++ |
| Water recovery estim. [kg/h] | 350 | 500 | 900 |
| Energy recovery [% dryer load] | 28 % | 53 % | 64 % |
| To dryer [kW] | 200 | 200 | 1600 |
| Process liquids [kW] | 250 | 250 | |
| Aux. heating [kW] | - | 400 | |
| Electrical power [kW] | 19 | 21+ | 570 |
| ROI [years] | 1.5-2.5 | 1-2 | 4 - 8 |
A suitable simulation environment is an important step in screening different markets' decarbonization potential against most viable commercial steps and integration levels. Figures 2 and 3 below are the output of this tool and propose ROIs based on input on dryer sizing, -operating conditions, -temperature setpoints as well residual energy sinks and – not least - local utility costs.
Figure 1. ROI analysis based on a simulation for the HRU 1-coil solution in Western Europe
/>
Figure 2. ROI analysis based on a simulation for integration level using hybrid high-temperature heat pump dryer using natural refrigerants and coupled to the dual-coil HRU system. Western Europe.
/>