Freeze-drying is a process for drying products without altering their qualitative and quantitative composition. It is a technique consisting of freezing and subsequent removal of water in the form of steam to obtain a dry product. Freeze-dried products can be stored for long periods of time while maintaining their physical, chemical, biological and organoleptic properties. This process is carried out under vacuum and at low temperature, which requires high energy consumption, an aspect that is a determining factor when assessing the viability of any freeze-drying project and which leads freeze-drying companies to seek industrial solutions with the best possible energy efficiency.

In terms of optimising energy consumption, there are several ways to improve the freeze-drying process to make it more efficient. Although the design and selection of the freeze-drying equipment influences the energy efficiency, the parameters to be taken into account in order to achieve the highest energy savings are:

  • Optimisation of freeze-drying parameters.
  • The use of more efficient cooling technologies.
  • Heat recovery.
  • Proper insulation of freeze-drying chambers and precise control of air flows to contribute to higher energy efficiency.
Freeze dryer for development

Choosing the right freeze dryer is critical to reducing energy consumption. We find that research and development freeze dryers are used on the market for production tasks that will never be cost-effective from an energy point of view, as they are designed to evaluate processes and extract data to optimise a recipe or analyse the feasibility of a given product. And vice versa, production machines where processes are developed.

Once the most appropriate equipment has been selected for the material to be freeze-dried and the quantity to be produced has been analysed, weighing up the cleaning and sterilisation systems, we will go on to evaluate the optimisation of the working parameters.

Optimisation of freeze-drying parameters

Graph freeze drying process.

The impact of freeze-drying conditions on the energy consumption of the process depends on several parameters:

  • The freezing temperature. An ideal freezing temperature means lower energy consumption as faster freezing reduces the time needed for sublimation.
  • The pressure in the freeze-drying chamber. The pressure in the chamber of the freeze-drying equipment is also crucial. Low pressure can be contrary to fast sublimation, so it must be balanced with the requirements of the product to be freeze-dried.
  • The sublimation rate of the ice. For the freezing rate it is especially important to know the eutectic temperature of the product if it is crystalline, or the glass transmission temperature if it is amorphous.
  • The efficiency of the refrigeration system. The rate of ice sublimation is closely related to the heat transfer and efficient operation of the refrigeration system. A precise design of the refrigeration system that minimises heat losses and maximises heat removal during sublimation can improve energy efficiency. In addition, the design of the refrigeration cycle and the selection of refrigerants can influence energy savings during the process.

The use of more efficient cooling technologies

Efficient refrigerated freeze dryer for food and chemicals

Some of the most efficient cooling technologies used in freeze dryers include:

  • Absorption refrigeration. This type of cooling uses a combination of heat and an absorber to transfer heat from one place to another. It is an efficient and cost-effective technology, but can be bulky and require regular maintenance.
  • Compression cooling. This type of refrigeration is the most common in freeze dryers. It uses a compressor to compress a gas which is then used to transfer heat. It is an efficient system, but can be noisy and generate waste.
  • Evaporative cooling. This method of cooling uses the evaporation of a liquid to absorb heat. It is an efficient and quiet technology, but may require regular maintenance.

The use of more efficient cooling technologies in freeze dryers offers significant benefits in industrial production:

  • Reduction of energy costs. Refrigeration is one of the main sources of energy consumption in freeze dryers. The use of advanced cooling technologies helps to reduce energy costs significantly.
  • Improved product quality. The more efficient cooling system reduces the formation of ice crystals during the freeze-drying process. This can help improve product quality and extend shelf life.
  • Increased operational flexibility. Modern refrigeration techniques have an impact on energy conservation, so freeze dryers can operate at lower temperatures. This can help manufacturers expand the range of products they can freeze-dry.

The design of environmentally friendly freeze dryers and production processes is a growing trend in the freeze-drying industry. As energy costs continue to rise and manufacturing conditions must adapt to increasingly demanding regulations, manufacturers are investing in technologies to reduce energy consumption.

Heat recovery in the freeze-drying process

Barnalab freeze-dryer for freeze-drying foodstuffs.

Heat recovery is a phase that uses waste heat from one process to heat a different fluid or process. In the case of freeze dryers, waste heat is generated during freezing and sublimation.

The reuse of energy in freeze dryers is highly beneficial:

  • Reduction of energy costs. Heat recovery reduces the energy consumption of a freeze dryer. This is because the waste heat is used to heat the process fluid, so there is no need to use an external heat source.
  • Improved efficiency. The heat integration process has an impact on the efficiency of the freeze-drying machine as waste heat that would otherwise be wasted is utilised.
  • Reduction of emissions. The reuse of thermal energy by the freeze dryer reduces greenhouse gas emissions.

There are different ways to recover heat in freeze dryers. One common way is to use a heat exchanger to transfer waste heat from one process to another. Another method is the use of a system to condense the water vapour that is generated during the dehydration process.

The industry’s awareness of eco-efficiency means that companies specialising in the manufacture of freeze-dryers or contract freeze-drying services are working towards sustainability on a daily basis.

Below are some specific examples of how heat can be recovered in freeze dryers:

  • Heat recovery from condensation. The water vapour generated during the dehydration process can be condensed to recover heat. This can be used to heat the process fluid, circulating air or cooling water.
  • Heat recovery from compression. The compressor used to compress the refrigerant gas generates energy. This is also used to heat the process fluid, circulating air or cooling water.
  • Evaporative heat recovery. The liquid used to absorb temperature in an absorption refrigeration system generates heat when it evaporates. As in the previous cases, it is used in the process of heating fluids, circulating air or cooling water.

The reuse of energy in freeze dryers is a complex technology that requires careful design. As experts in freeze-drying services for third parties, at Barnalab we apply this technology to optimise consumption in the manufacture of our freeze-dryers and in the design of the freeze-drying processes. In addition, our facilities have solar panels to reduce electricity consumption and incorporate 24v continuous electrical resistances.

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