28, Apr 2020 / rebound

Optimizing Blast Freezing in Food Production

In 2018, China imported 12.6 billion pounds of frozen beef, almost all of which, prior to arrival, was processed, packaged, loaded onto pallets and then frozen in blast cells. This batch freezing process, whereby anywhere from 30-200 pallets are loaded into a giant room and left to freeze, is one of the least efficient methods for removing heat and yet is the standard freezing process for most industrial level food production operations.

Batch blast freezing requires careful optimization of equipment, electricity, and labor expenditures. Unfortunately, each of these inputs continue to be used inefficiently due to one critical pain point – a blast freezing process wastes time. In fact, the inability to accelerate blast freezing cycles to meet growing demand is an enormous source of frustration for operations professionals tasked with throughput improvement.

These operators are aware that during the first 30% of a freeze cycle, there is so much heat to be removed from those pallets that facility engine rooms fail to maintain setpoint suction temperatures. This slows the process down. Unfortunately, they are also aware that it doesn’t make economic sense to install refrigeration capacity that’s going to be utilized 30% of the year, just to meet that peak need.

All parties want more product throughput, but that desire is economically out of reach, and there are fundamental infrastructure obstacles standing in the way.

Why this capacity constraint slows down blast freezing facilities.

Poor utilization: Early in the blast freezing cycle, the compressors limit the process speed because so much heat is coming off the product that they can’t maintain suction pressure. At the end of the cycle, the process is limited by conduction through the palletized product so compressor capacity is underutilized.

Poor economics: In batch freezing, installing sufficient compressor capacity to meet peak heat loads results in poor annualized asset utilization because that extra, low-temperature booster compressor will only be used 30% of the year. And unless companies purchase expensive variable speed drives, the vapor compression system suffers an efficiency and maintenance penalty for partial load operation. Additionally, blast cell evaporators are undersized due to cost, so instead additional fan power is used to increase air velocity over the coils, shifting what was a capital cost to operational cost. Not ideal.

Poor understanding: There is a misconception that airflow, spacing and packaging are the key to accelerating freeze times. It’s true that if these parameters are improved there will be more heat removed from the product, but that only shifts the heat transfer bottleneck to the refrigeration system. Pallets have a quantity of heat that must be removed from the blast cell. This requires low air temperatures, which requires low suction temperatures, which in turn requires sufficient compressor capacity. Air flow, spacing and packaging alone do not solve the entire heat removal process.

Three ways to alleviate capacity constraints, technically, with vapor compression.

Stop batch freezing: Start continuous freezing and packaging afterwards. Heat loads associated with continuous freezers are far more consistent and manageable. That said, while thermodynamically more practical, there are mechanical stresses and defrost consequences associated with tunnel and spiral freezers.

Start from scratch: Spend the money to properly design blast cells. There are smart teams working on complex air flow CFD models to address pallet placement and evaporator locations. A non-ideal scenario is slapping walls around a fan bay with some extra fan power and assume that freeze times will be solved. This only fixes a secondary problem though, and can’t fix compressor capacity utilization.

Deploy Additional Capacity: Installing a low pressure booster compressor, the needed high pressure capacity and the associated condenser capacity will indeed accelerate freeze times by meeting peak heat load. However, will that pass through a capital expenditure process? Unlikely (see below).

Why vapor compression can’t economically solve blast freezing issues.

Adding capacity to improve blast freezing times is rarely the economically optimal choice and thus will fail most capital expenditure processes, particularly for providers of third-party blast freezing services whose customers will rarely sign long-term contracts to feed continuous inbound pallets.

Compressors: Assuming the engine room space exists, an organization could install all the added infrastructure to ensure that blast freezing temperatures always remain at -40°F.Unfortunately, that capacity might only be used 30% of the year to meet those peak heat loads. The payback on that utilization won’t be attractive. Additionally, the total compression capacity expansion cost must be considered. This includes not just a booster compressor, but the addition of any high-pressure compression needs.

Condensers and piping: Once compressor capacity is solved, the facility must ensure the condensers are sufficiently sized, all infrastructure is re-piped and the cost of all associated downtime is quantified.

Evaporators: Sufficient engine room and condenser capacity won’t be useful if the blast cell evaporators don’t have sufficient surface area or air velocity.

Why every facility blast freezing pallets should consider IcePoint capacity to accelerate freezing, immediately.

IcePoint represents a new method to accelerate blast freezing by providing a burst of cooling during the beginning of the blast freezing process, when its needed most.

It’s agile: The ability to ramp a 28 TR system up to 140 TR of -40°F capacity means IcePoint can provide bursts of capacity to immediately manage any peaks in heat load. IcePoint automatically stores excess capacity to inject it into the process when it’s needed most. That means low low temperature suction pressures will be achieved, always.

It’s utilized: As pallet inbounds fluctuate, IcePoint adjusts operationally. Use IcePoint as a booster during peak inbound periods or as baseload capacity when inbounds dip.

It’s packaged: Avoid the downtime and cost of a complete engine room re-work. Install IcePoint skids outside of the facility and pipe to either A) a diffusion bonded plate heat exchanger in the engine room or B) a brine air handler on the roof.

It’s a revenue booster: It has a higher COP than 2-stage ammonia systems, it doesn’t suffer from part-load inefficiencies and demand charges on hot summer days can be mitigated while also controlling moisture. But most importantly, customers reduce blast cycle times by avoiding spikes in blast cell air temperatures, which lead to additional pallets frozen annually, which boosts top line revenue.

Optimizing blast freezing requires agile refrigeration capacity.

Chinese beef imports are highlighted to emphasize A) the magnitude of blast freezing occurring globally and B) the significance plays in the global food trade economy. However, whether its beef, poultry, pork, seafood, fruit or other food product, the excessive time it takes to blast freeze product remains an industry-wide struggle. As an example:

Regardless of product, suction pressures are still going to jump from 0 psig to 25 psig during the first 30% of a blast cycle even though engine room compressors are running fully loaded.

Compressors will still idle or run partially loaded while pallets in one corner of a blast cell wait to freeze due to receiving 40% less air flow.

And retrofit projects to rebalance air flow of existing blast cells will be proposed, along with adding new compressors, all in an attempt to decrease cycle times and freeze more product. These projects will all be rejected because >5 year paybacks aren’t feasible.

In the end, the only way to eliminate the time constraint, economically, is to provide the exact amount of refrigeration needed, at the exact time its needed. IcePoint capacity provides this resource, helping blast freeze pallets in 10% less time. The resulting 10% increase in annualized throughput is a non-trivial boost in profitability at a superior payback of 2-year or less.