How to Pass the Ice Crystal Band in Crayfish Quick-Freezing: Configuration Approach of the DKN-LFT-1212 Tunnel Line

<img class="product-hero" src="/images/articles/crayfish-ln2-tunnel-cell-integrity-01.jpg" alt="How to Pass the Ice Crystal Band in Crayfish Quick-Freezing: DKN-LFT-" loading="lazy"> <p>A domestic crayfish processing enterprise produces cooked shell-on crayfish and peeled shrimp meat, in both IQF and block-frozen forms, with a center temperature requirement below -18℃. The quality divide is not at the final temperature but at the speed of passing through the -1℃ to -5℃ segment: move too slowly, and intercellular ice crystals grow large; after thawing, juices run out and the shrimp meat turns dry and tough. Comparable capacity is matched by the DKN-LFT-1212 liquid nitrogen quick-freezing tunnel line, mesh belt 12000 × 1200 mm, no-load cooling 10℃ per minute, temperature control accuracy ±2℃.</p> <p><img src="/images/articles/crayfish-ln2-tunnel-cell-integrity-02.jpg" alt="Liquid nitrogen quick-freezing tunnel line workshop conveyor section"></p> <h2 id="i-application-background">I. Application Background</h2> <p>Crayfish orders concentrate in peak season, and the workshop schedules production at peak levels, with cooking, cooling, freezing, and packaging running in sequence. There are three product forms: cooked shell-on whole crayfish, peeled shrimp meat, and frozen blocks packed by specification. IQF requires individual pieces separated and non-sticking; block freezing requires neat arrangement within the block and no scattering after thawing.</p> <p>Cooked materials enter the freezing section with residual heat and surface moisture; if the cycle cannot keep up, both upstream and downstream processes back up. Processing requirements can be summarized in three points: center temperature reached, low thaw drip loss, and intact IQF pieces.</p> <h2 id="ii-process-difficulties">II. Process Difficulties</h2> <p><strong>The time to pass through the ice crystal band determines the degree of cell damage.</strong> As the material moves down from 0℃, -1℃ to -5℃ is the range where a large amount of water freezes. With a long residence time, ice formed first outside the cells draws water out from inside the cells, ice crystals grow in the gaps, and burst the cell walls; on thawing, the damaged spots become channels for juice to flow out.</p> <p><strong>Shrimp meat is more sensitive to slow freezing than whole crayfish.</strong> Peeled shrimp meat has no shell as a buffer, muscle fibers are directly exposed, and surface moisture is high; after slow freezing, water accumulation in the thawing tray is obvious, and the sense of moisture loss after reheating is heavier.</p> <p><strong>Surface moisture causes sticking.</strong> When wet material enters the tunnel, water vapor frosts in the low-temperature zone and falls on the mesh belt and product surfaces. If surface moisture is not controlled, IQF products tend to stick into clumps after discharge and require manual separation during packing.</p> <p><strong>The cycle must be measured with product loaded.</strong> No-load cooling of 10℃ per minute is an equipment capability indicator; after loading, it is affected by load, layer thickness, and inlet temperature, and the actual cooling curve differs from no-load. Production scheduling cannot directly derive time from no-load figures.</p> <h2 id="iii-solution-configuration">III. Solution Configuration</h2> <p>This scenario is matched by the <strong>DKN-LFT-1212 liquid nitrogen quick-freezing tunnel line</strong>, with main parameters as follows (quoted from product technical documents):</p> <table> <thead> <tr> <th style="text-align: left">Item</th> <th style="text-align: left">Parameter</th> </tr> </thead> <tbody> <tr> <td style="text-align: left">Tunnel mesh belt</td> <td style="text-align: left">12000 mm (total length) × 1200 mm (width)</td> </tr> <tr> <td style="text-align: left">External dimensions</td> <td style="text-align: left">12000 × 2250 × 1670 mm</td> </tr> <tr> <td style="text-align: left">Working temperature</td> <td style="text-align: left">-150℃ ～ room temperature</td> </tr> <tr> <td style="text-align: left">Temperature control accuracy</td> <td style="text-align: left">±2℃</td> </tr> <tr> <td style="text-align: left">Cooling rate</td> <td style="text-align: left">No-load cooling 10℃ per minute</td> </tr> <tr> <td style="text-align: left">Freezing capacity</td> <td style="text-align: left">1 m³/h</td> </tr> <tr> <td style="text-align: left">Total power</td> <td style="text-align: left">18 kW</td> </tr> <tr> <td style="text-align: left">Refrigerant</td> <td style="text-align: left">5-8 BAR liquid nitrogen (liquid nitrogen tank self-provided)</td> </tr> <tr> <td style="text-align: left">Oxygen concentration monitoring</td> <td style="text-align: left">Oxygen concentration setpoint 19.5%-21.5%</td> </tr> </tbody> </table> <p>The configuration logic looks at three points. The mesh belt total length of 12000 mm provides space for three stages: inlet pre-cooling, deep freezing, and outlet temperature equalization; material residence time is adjusted by belt speed. The mesh belt width of 1200 mm corresponds to side-by-side tray placement or direct rack entry, accommodating both thin-spread IQF and whole-tray block freezing. Total power is 18 kW; the electrical portion covers only drive, fans, and control system, while cooling capacity is provided by liquid nitrogen; the power distribution capacity is checked against site conditions and subject to order confirmation.</p> <p>External dimensions 12000 × 2250 × 1670 mm are the cabinet itself; workshop floor marking must also reserve loading position, receiving and transfer position, and maintenance space on both sides.</p> <h2 id="iv-process-points">IV. Process Points</h2> <p><strong>The endpoint is the center temperature.</strong> -150℃ to room temperature is the equipment range, not the discharge target. Before discharge, measure the geometric center: for block freezing, measure the block center; for shell-on whole crayfish, measure the head-thorax junction. Temperature control accuracy ±2℃ keeps the setpoint stable, so discharge conditions at different times within the same batch are comparable.</p> <p><strong>Control surface water before loading.</strong> After cooking, drain and spread to air until no water drips from the surface before entering the tunnel; this helps reduce frosting in the low-temperature zone and IQF sticking.</p> <p><strong>Belt speed is the main adjustment parameter.</strong> When changing specifications, adjust belt speed rather than temperature setpoint; keep temperature stable and adapt to different loads and thicknesses through residence time. For each specification change, run a loaded cooling curve and record the time for center temperature to reach -18℃ as the basis for production scheduling.</p> <p><strong>Oxygen concentration monitoring is a mandatory configuration.</strong> Vaporized liquid nitrogen displaces oxygen in the tunnel; the setpoint is 19.5%-21.5%, with monitoring points covering the loading end and discharge end. Ventilate and displace before shutdown for maintenance.</p> <p><strong>Discharge goes directly into the cold chain.</strong> Frozen material does not stay in the workshop; it goes directly to frozen storage or packaging stations below -18℃ to avoid surface temperature rise and recrystallization.</p> <h2 id="v-suitable-users-and-selection-advice">V. Suitable Users and Selection Advice</h2> <p>This configuration suits crayfish processing and aquatic product processing enterprises with relatively fixed product forms, continuous daily production, and mainly IQF or whole-tray block freezing. To judge tunnel type versus cabinet type, look at two points: whether there is stable output for several continuous hours each day, and whether the workshop can provide a straight-line in-and-out material flow. For small batches, frequent variety changes, and only one room, cabinet type is more suitable; for continuous output where upstream and downstream are themselves assembly lines, the tunnel line can run.</p> <p>For tunnel line parameters, see the <a href="/en/products/dkn-lft-1212/">Liquid Nitrogen Quick-Freezing Tunnel DKN-LFT-1212 product page</a>; for freezing curve principles, see <a href="/en/tech/freezing-curve-and-ice-crystal-band/">Freezing Curve and Maximum Ice Crystal Band</a>; for belt speed calculation, see <a href="/en/tech/ln2-tunnel-freezing-cycle-and-belt-speed/">Tunnel Freezing Cycle and Belt Speed Setting</a>. To check configuration against your own product specifications and workshop conditions, you can <a href="/en/contact/">contact us</a>.</p> <h2 id="faq">FAQ</h2> <h3 id="why-emphasize-the-speed-of-passing-through-the--1-to--5-segment">Why emphasize the speed of passing through the -1℃ to -5℃ segment?</h3> <p>This range is the temperature band where most of the water in the material freezes. The longer the residence time, the larger the ice crystals grow in the intercellular spaces, the more the cell structure is burst, and on thawing the juice flows out from the damaged spots.</p> <h3 id="can-no-load-cooling-of-10-per-minute-be-used-directly-to-calculate-output">Can no-load cooling of 10℃ per minute be used directly to calculate output?</h3> <p>No. This is the cooling capability under no-load conditions. After loading, it is affected by load, layer thickness, and inlet temperature, and the actual cooling rate is lower than the no-load value. Production scheduling should be based on measured loaded curves, combined with belt speed and mesh belt length, to calculate the actual residence time of material in the tunnel.</p> <h3 id="what-is-the-difference-between-iqf-and-block-freezing-in-equipment-settings">What is the difference between IQF and block freezing in equipment settings?</h3> <p>The difference lies in placement method and belt speed. IQF requires pieces spread out and not touching, with a thin layer and relatively fast belt speed; block freezing is whole trays or boxes entering the tunnel, with a thick layer, requiring a longer residence time for the block center to reach below -18℃.</p>