Antarctic krill, as one of the crustacean resources with the largest biomass in the world, has an annual catchable amount of over 50 million tons. Its characteristics of high protein (16%-20% content) and high unsaturated fatty acids make it an important source of aquatic feed, functional food, and pharmaceutical raw materials. However, within 2 hours after being caught, krill will deteriorate due to the sharp increase in the activity of endogenous enzymes (such as proteases and lipases), and its initial moisture content is as high as 80%-85%. Traditional hot air drying is prone to protein denaturation, flavor deterioration and other problems, while disc dryers, relying on the technical characteristics of precise temperature control and heat exchange, efficient dehumidification, and gentle material handling, have become the core equipment for industrialized drying of krill. Their application efficacy is as follows:​

I. Core Technical Requirements for Krill Drying​

Krill drying needs to meet three key indicators simultaneously:​

  1. Microbial safety: The water activity (Aw) needs to be reduced to below 0.6 (corresponding to a moisture content of ≤12%) to inhibit the reproduction of halophilic bacteria and spoilage bacteria, and in the process, it is necessary to avoid excessive histamine and other biogenic amines caused by high temperatures (EU standards require ≤100mg/kg);​

  2. Nutrient retention: Phospholipid-type Omega-3 (with a total EPA+DHA content of 15%-20%) is easily oxidized at temperatures above 60℃, so it is necessary to control the actual heating temperature of materials to ≤55℃ through equipment structure design;​

  3. Processing adaptability: After drying, krill needs to maintain the integrity of cell structure to avoid the mixing of impurities during subsequent deep processing (such as enzymatic hydrolysis) caused by crust breakage, and the breakage rate must be ≤3%.​

Traditional hot air drying, due to direct contact with hot air, has three major drawbacks: first, large local temperature fluctuations (±5℃) easily cause overheating of some krill; second, when the air flow rate is ≥1.5m/s, it is easy to cause crust damage; third, the energy consumption is as high as 800-1000kWh/ton, which is much higher than the industry energy efficiency standards.​

II. Technical Adaptability of Disc Dryers​

Through the combined design of conduction heat exchange modules and intelligent graded temperature control systems, disc dryers adopt Mitsubishi's unique steam heat exchange technology and are adapted to 0.5-0.6MPa saturated steam as the main heat source. The disc adopts a low rotation speed and uses the gentle radiant heat exchange of the 159℃ heating surface for slow dehydration. The rake leaves adopt a bionic arc design (imitating the natural accumulation form of krill), which can avoid cell rupture of high-moisture materials caused by violent stir.​

The edge of the disc is made of wear-resistant self-lubricating alloy, with a gap of 8-10mm from the machine shell. Combined with food-grade silicone scrapers, it can gently peel off the adhering materials and avoid mechanical damage to the krill crust. In actual operation, the breakage rate of dried products can be controlled below 1.8%, which is much better than the 8%-10% breakage rate of spray drying. At the same time, the equipment is equipped with an online monitoring system for material integrity, which can feedback the breakage rate data in real time and automatically adjust the rotation speed of the rake leaves.​

III. Technological Innovations of Disc Dryers in Krill Drying​

In view of the special scenarios of krill fishing and processing (such as limited space on processing ships, easy spoilage of raw materials, corrosion in high-salt environments, etc.), disc dryers have achieved a number of targeted innovations in technology:​

  1. Compact integrated design: Adopting a vertical multi-layer superimposed structure, the floor area of traditional horizontal equipment is reduced by more than 60%. A single equipment can be directly installed under the deck of the processing ship, solving the problem of limited space on ocean-going processing ships. At the same time, the equipment forms a modular unit with the steam generator and condensation recovery system, and the installation and commissioning cycle is shortened to 72 hours, which can meet the needs of rapid production during the fishing season.​

  2. Anti-corrosion and sanitary modification: The core contact parts (disc, rake leaves, inner wall of the machine shell) are all made of ultra-low carbon austenitic stainless steel (316L), treated by electrolytic polishing (surface roughness Ra≤0.8μm), and the salt spray corrosion resistance reaches C5-M grade (in line with ISO 12944 standard), which can operate continuously for 5000 hours in a marine environment with a salt content of 3.5% without obvious rust. In addition, all dead corners in the equipment adopt arc transition design, equipped with CIP online cleaning system (cleaning pressure 3-5bar, water temperature 80-85℃), and the cleaning residual rate is ≤0.01mg/cm², meeting the FDA food contact material standards.​

  3. Intelligent linkage control system: Integrating multi-parameter sensors (including infrared moisture meter, platinum resistance temperature sensor, torque sensor), it collects real-time data such as material moisture content (accuracy ±0.5%), heating surface temperature (±1℃), and rake leaf load, and links with the fishing amount metering device through the PLC system: when the fishing amount suddenly increases (such as more than 12 tons per hour), it automatically increases the steam pressure to 0.6MPa and speeds up the rotation speed of the rake leaves; when a material corruption risk is detected (histamine concentration ≥30mg/kg warning), it triggers over-temperature protection and starts the emergency drying mode to ensure product safety.​

Disc dryers have promoted the transformation of krill processing from "extensive drying" to "precision preservation", providing key technical support for the efficient utilization of Antarctic biological resources.​