Air Dryers in Food Processing

By PMG Engineering · 6 Mar 2020

In food processing plants, compressed air often contains moisture that can adversely affect product quality by causing contamination, microbial growth, and corrosion in processing equipment. To maintain hygienic food manufacturing standards, it is crucial to remove moisture before compressed air comes in contact with food products. Air dryers play a vital role in ensuring moisture-free air, preventing issues like rusting in tanks, emulsification with grease, and washing out lubrication oils.

Applications of Air Dryers in Food Manufacturing

Compressed air has a higher water vapor content than atmospheric air, which can lead to condensation in pipelines, corrosion of equipment, and microbial growth (e.g., mold and fungus). This negatively impacts food safety, product shelf life, and equipment efficiency.

Air dryers remove moisture from compressed air using different technologies, ensuring the required pressure dew point (PDP). A lower PDP value signifies reduced moisture content, making the air safer for food processing applications.

Types of Air Dryers for Food Processing Plants

Air dyers are broadly categorized into primary and secondary types, depending on their dew point performance. The four major types are:

1. Regenerative Desiccant Air Dryer

Uses activated alumina, silica gel, or molecular sieve to absorb moisture.
Operates with two pressure vessels (towers): one drying tower and one regenerative tower.
The saturated desiccant bed is purged using compressed air, maintaining continuous moisture removal.
Suitable for high-purity food processing applications.

2. Refrigerated Air Dryer

Uses two heat exchangers (air-to-air and air-to-refrigeration) or a single combined exchanger.
Common refrigerants include R-134a, R-410a, and in older models, R-22, R-404a.
Provides a dew point of approximately 35°F (2°C), preventing excess condensation.
Ideal for general-purpose food manufacturing applications.

3. Deliquescent Air Dryer

Consists of a pressure vessel filled with a hygroscopic medium that absorbs water vapor.
The medium dissolves, forming a liquid that must be drained and replenished regularly.
Provides dew point suppression of about 20°F (11°C) below compressed air temperature.
Used in low-maintenance food factory setups.

4. Membrane Air Dryer

Uses a coalescing filter to remove liquid water, oil, and particulates.
A partial flow of dried air is expanded and passed in a counterflow direction to flush out moisture.
Energy-efficient and suitable for sensitive food industry applications.

Choosing the Right Air Dryer for Food Industry Applications

It is not always necessary to operate at the lowest pressure dew point, as this can be economically unfeasible. It is always recommend to select an air dryer based on the degree of dryness needed for each application, considering operational costs and process requirements. By implementing the right air drying technology, food businesses can maintain hygienic food production standards, enhance equipment lifespan, and ensure regulatory compliance.

Frequently asked

Why does compressed air need drying in a food processing plant at all?

Compressed air carries a higher water vapour content than atmospheric air, and that moisture causes condensation in pipelines, corrosion of processing equipment and microbial growth such as mould and fungus. It also leads to rusting in tanks, emulsification with grease and washing out of lubrication oils. Removing moisture before the air contacts food protects product quality, shelf life and equipment efficiency in hygienic food manufacturing.

What is pressure dew point and should we always aim for the lowest one?

Pressure dew point (PDP) indicates the moisture content remaining in compressed air; a lower PDP value means less moisture and safer air for food processing. However, operating at the lowest possible PDP is not always necessary and can be economically unfeasible. PMG Engineering recommends selecting an air dryer based on the degree of dryness each application genuinely needs, weighing operational costs against process requirements.

Which type of air dryer suits high-purity food processing?

A regenerative desiccant air dryer is suited to high-purity food processing applications. It uses activated alumina, silica gel or molecular sieve to absorb moisture and operates with two pressure vessels or towers, one drying and one regenerating. The saturated desiccant bed is purged using compressed air, which maintains continuous moisture removal without interrupting supply to the process.

What dew point can we expect from a refrigerated air dryer?

A refrigerated air dryer provides a dew point of approximately 35°F (2°C), which is sufficient to prevent excess condensation and makes it ideal for general-purpose food manufacturing applications. It uses two heat exchangers, air-to-air and air-to-refrigeration, or a single combined exchanger. Common refrigerants include R-134a and R-410a, while older models used R-22 and R-404a.

How does a deliquescent dryer differ, and what maintenance does it need?

A deliquescent air dryer is a pressure vessel filled with a hygroscopic medium that absorbs water vapour. The medium dissolves into a liquid that must be drained and replenished regularly. It offers dew point suppression of about 20°F (11°C) below the compressed air temperature, which suits low-maintenance food factory setups where deep drying is not required.

Is there an energy-efficient option for sensitive food applications?

A membrane air dryer is energy-efficient and suitable for sensitive food industry applications. It uses a coalescing filter to remove liquid water, oil and particulates, then expands a partial flow of the dried air and passes it in a counterflow direction to flush moisture out of the membrane. This gives continuous drying with minimal moving parts.

CITE THIS

PMG Engineering. (2020). Air Dryers in Food Processing. PMG Engineering. https://pmg.engineering/Article/30/air-dryers-in-food-processing/

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