A significant and critical point is selecting a suitable compressed air dryer for each production unit.

In addition to the waste of capital, the non-expert selection of air dryers can lead to stoppages in production lines.

In selecting an air dryer, the first question that should be asked is how free of humidity the compressed air is required.

Obviously, the higher the expectation of accuracy and quality of filtration, the higher the cost.

The next important question is what paths does the compressed air take after production? Do the pipes pass through the open space?

What changes does the climate face in different seasons of the year? Does it get below zero °C?

All these questions are asked to be able to answer a decisive question, which is, what the dew point should we expect from our dryer?

Refrigeration dryers are not able to provide the dew point below zero. Suppose the climate temperature goes below zero °C. In that case, there is a possibility of freezing the remaining humidity in the lines, which causes the compressed air-consuming systems to stop and cause possible damage.

Compressed air quality in terms of being free from humidity depends on the choice of the dew point. The lower the dew point, the drier the air will be. Refrigeration dryers do not have the possibility of providing the dew point below zero °C. We must use absorption dryers if we want the dew point below zero or drier air without humidity.

By offering a different product called absorption dryer, we can provide humidity-free compressed air up to the dew point of -40 °C

The operation of way absorption dryers is based on the scientific phenomenon of surface absorption. Compressed air is passed over the surface of another material, the humidity-absorbent material, and the humidity in it is trapped. This physical surface absorption is a reversible process. In this type of absorption, we do not have a chemical reaction. The absorbed molecules are only collected on the absorbent surface.

Absorption dryers absorb air humidity by using absorbent materials used in their structure, and after a period of humidity absorption, the absorbent materials reach the breaking point or saturation point. Any adsorbent bed becomes saturated after a period of operation, its absorption capacity is filled, and there is no more room for new molecules. In such a case, the process of desorption or regeneration should be done.

Desorption processes are endothermic; thermodynamically, high temperature and low pressure favor them. Process experts have used this point in the industry and implemented PSA and TSA processes to regenerate adsorbents in desiccant dryers.

Considering that raising the pressure increases the efficiency of the absorption phenomenon, for the desorption phenomenon, it is necessary to lower the pressure so that the desorption process takes place. The adsorbent is regenerated, which a physical phenomenon is called PSA.

As the temperature decreases, the absorption process is better, so the desorption process, which is the reverse process, will have higher efficiency for regenerating the adsorbent as the temperature increases.

The engineering design department of Roll Air Company, with knowledge of the isotherm properties of absorbent materials available in the industry, as well as the analysis of the behavior equation of absorbents, has chosen absorbent materials according to the type of use of the air dryer and using related software, the amount of absorbent in the unit of time has extracted.

These dryers are equipped with two cylinders or two tanks under pressure, which are called towers.

These two towers are installed next to each other on a chassis vertically and parallel to each other. Both towers are filled with humidity-absorbing materials and according to the arrangement of the humidity-absorbing grains, from the large size at the bottom of the tower to the smaller grains at the top of the tower. Compressed air is trapped by passing through the bed of absorbent material layers. After a certain time of humidity absorption, the absorbent materials are saturated.

At this time, automatic valves direct the air to the next tower. At the same time as the dehumidification process starts in the second tower, the regeneration or desorption process starts in the first tower. When the second tower is saturated, the humid compressed air is again directed to the first tower and the regeneration operation of the second tower takes place, and this process is done continuously during the operation of the absorption dryer.

In the compressed air industry, two techniques are used for the adsorption process of adsorption dryers.

• Pressure Swing Adsorption (PSA): Another name for this regeneration technique is purge regeneration
• Temperature Swing Adsorption (TSA): Another name for this regeneration technique is heated regeneration.

This model of dryers takes about 15% of the dry compressed air from the online tower (the tower involved in the absorption process). After expanding and lowering the pressure of this dry air, it is sent to the offline tower (the tower in regeneration mode). The dry air becomes drier due to the decrease in its pressure, and its capacity to accept humidity increases; after this dry air passes through the bed of absorbent materials, the humidity is removed from the tower involved in the regeneration process (offline tower).

In this method, we use the technique of heating absorbent materials to regenerate the towers.

By heating the humidity absorbent materials, the weak van der Waals forces between absorbent and absorbed molecules, which are very weak, are broken, and humidity is removed from the humidity absorbent materials that have accumulated on their surfaces.

In the heated regeneration method, a part of the output air of the online tower (the tower involved in dehumidification) is branched and expanded to near atmospheric pressure. After passing it through the heater, its temperature is raised between 150 and 180 °C. We pass this heated air through the bed of absorbent materials in the opposite direction of the absorption stage, i.e., from top to bottom. In this way, the humidity is released and directed out of the device.

As we can see, the difference between warm and purge regeneration methods is in the application of thermal energy to the air entering the tower in regeneration mode in order to transfer and remove humidity. The application of this thermal energy leads to an increase in the humidity absorption capacity of dry air. As a result, the regeneration rate, as well as the consumption of dry compressed air, is reduced.

One of the advantages of the purge regeneration method is the minimal consumption of electrical energy.

Both methods have advantages and disadvantages; the choice of each of these two methods or two devices should be based on the type of use and the facilities available for operation, as well as the duration of work day and night and checking other available dryers on the line, be examined.

The total price of the dryer with the heated regeneration method is more expensive than the one with the dryer with the purge regeneration method.

The electrical energy consumption of the dryer with the purge regeneration is much less than that of the heated regeneration device.

Since the production of compressed air by the compressor requires spending money and the heated regeneration device uses less amount of dry air for regeneration, it provides more economical dry air during the time.

The regeneration operation is done using dry expanded air (Purged) from the online tower. In this method, about 15 to 20% compressed air free of humidity and pressure of 7 bar is required for regeneration.

This dryer model is suitable for low-consumption capacities.

The regeneration operation is done using dry expanded air (Purged) from the online tower. In this method, about 15 to 20% compressed air free of humidity and pressure of 7 bar is required for regeneration.

This dryer model is suitable for low-consumption capacities.

In businesses, it is very important to produce a product at a total and competitive price. This happens when it is possible to concentrate as much as possible on the energy consumption and spare parts of machines and increase the lifespan of production-related devices. Roll Air Company's life depends on its customers' life and development, which is why we help preserve the customers' capital by using the best spare parts and design based on the long life of the devices

The screw compressors of this company are equipped with a closed input suction filter and with a propylene housing that is resistant to impact and corrosion-resistant and designed for harsh working conditions, such as in places with high dust and even high temperature, and guarantees the air input free from suspended particulates and dust to the air-handling unit. Among the advantages of this filtering, the unit can be mentioned as long life thanks to efficient and reliable elements and low-pressure drop.

The use of an efficient air filter does not allow dust to enter the air-handling unit, and following this point will prevent dust from entering the bearings, rotors, heat exchangers, and other parts related to air and oil, as well as increasing the life of the oil, and the air-oil separator filter and oil filter guarantee the longevity of the bearings

Unlike other absorption dryer models, this device does not use dry air produced from the online tower or, in other words, the air produced by the compressor for regeneration.

The air is passed over an electric heater by a blower. After heating, it is directed to the offline tower that needs to be regenerated.

This device model consumes nearly 40% less energy than the HPRD model device.

The air around us contains water vapors, and the amount of these vapors is more in hot air and less in cold air.

When the air is compressed, the concentration of this water increases.

For example, suppose a compressor with a capacity of 12 m3/h sucks in environment air at a temperature of 20 °C and a humidity of 80% and takes it out under a pressure of 7 bar.

After leaving the compressor, the air is 100% saturated, humidity is condensed, and about ten l/h of water enters the compressed air line.

If this humidity is not removed, it can lead to corrosion of air transmission pipes, damage to the performance of pneumatic systems and electric valves, and even harm the process of manufacturing and production.

For this purpose, to avoid problems and damages caused by water penetration in lines and machines that consume compressed air, it is necessary to dry the air.

Compressed air dryers are one of the most important parts of the compressed air system. It doesn't matter where you are, in humid and hot areas or temperate or dry areas; the air in the atmosphere contains some water vapor.

When the air or gas cools to the point where it can no longer hold water vapor (passes the saturation point), it begins to condense into liquid water.

One of the ways to remove humidity from compressed air is to cool the air, which leads to condensation and separation of water from the air.

One of the most popular options for removing humidity is refrigeration dryers, which factories and industrial units have welcomed due to their ability to reach the acceptable dew point. By cooling the air, these dryers remove the humidity in the air and thus provide dry air.

Among the advantages of refrigeration dryers that have made them very popular, the following can be mentioned:

• Low initial cost and capital to purchase the device
• Relatively low operating cost and energy consumption
• Low maintenance cost and very low depreciation rate
• Safe against airborne oils and invulnerability of it

The work of refrigeration dryers is the same as home refrigerators, so a refrigerant lowers its temperature by absorbing the heat of compressed air.

The refrigeration dryer is equipped with a cooling cycle. The cooling compressor in the device injects the refrigerant gas under pressure into the condenser.

The pressurized and hot gas, after entering the condenser, gives its temperature to the environment and changes its phase, and becomes a liquid phase.

The liquid from the condenser enters the evaporator (heat exchanger), and its pressure decreases after absorbing the heat of the hot compressed air; it turns into a gas. This gas, which its pressure is reduced, is sucked again by the cooling compressor, and this cycle is repeated during the dryer's operation.

The design of refrigeration dryers is based on the design and use of two heat exchangers.

The heat exchanger exchanges the hot air with the cool air coming out of the dryer at the beginning of the compressor's compressed air entering the dryer.

Compressed air enters the second heat exchanger after initial pre-cooling. In this exchanger, the compressed air is cooled to about three °C by the refrigerant of the cooling cycle. This process causes humidity to condense and turn it into a liquid, leading to its exit from the compressed air.

The cooled and dried air re-enters the first heat exchanger and causes pre-cooling of the input hot air, and this heating of the dry air causes the outer part of the air transfer pipes not to sweat.

Important factors are involved in estimating the capacity and selecting refrigeration dryers. Their correction coefficients should be extracted from the tables and applied.

One of the most important parameters is the dew point. First, we must determine which dew point suits our work process.

Obviously, the lower the dew point we apply, the drier the air will be, which requires spending more money and energy, so knowing and selecting the exact dew point is very important.

The experts of the engineering department of Roll Air Company, according to their many experiences in calculating the dew point for different uses, after checking the working and climatic conditions of each customer, calculate and estimate the dew point, which in addition to providing acceptable air quality in terms of the quality class results in the optimal selection of the device and energy consumption according to the needs.

Among the factors that experts check to estimate the dew point, the following can be mentioned:

Extracting the environment temperature in the coldest climatic conditions that compressed air transmission pipes will encounter. Investigating the piping route of compressed air transmission in the entire production unit and estimating which points the compressed air popping lines pass through with the lowest temperature.

Examining the machines separately and considering what class of compressed air quality level they need based on the standard ISO 8573-1. Investigating the processes where the compressed air is directly related to the product and accurately estimating the air consumption class to be dry.

Among other important factors that should be taken into account and included in the accurate calculation of the choice of a refrigeration dryer are as follows:

• Maximum volume of air entering the dryer
• Maximum temperature of the air entering the dryer
• Maximum environment temperature
• Maximum input air pressure to the dryer
• Maximum allowable pressure drop of the dryer
• Required dew point pressure

Obviously, the capacity tables and technical specifications of refrigeration dryer manufacturing companies are based on standard conditions, and all correction coefficients should be included in them to choose the correct and appropriate dryer.

For example, the capacity tables and technical specifications of manufacturing companies are set based on these parameters, and correction factors should be applied and modified for the working conditions considered by each customer.

• The temperature of compressed air entering the device: 37.5 °C
• Environment temperature: 37.5 °C
• Input air pressure: 7 bar
• The dew point pressure temperature: 3 °C
• Minimum environment temperature: 4.5 °C

To provide distinguished and superior services, as well as to introduce audited products in terms of quality and energy consumption level, Roll Air Company has included important parameters in the selection and introduction of refrigeration dryer products so that, while guaranteeing the quality of compressed air, we can provide refrigeration dryers with optimal energy consumption and at the same time offer the lowest level of repair and maintenance costs to our respected customers.

• Maximum volume of air entering the dryer
• Maximum temperature of the air entering the dryer
• Maximum environment temperature
• Maximum input air pressure to the dryer
• Maximum allowable pressure drop of the dryer
• Required dew point pressure
• Advantages and features of refrigeration dryers of Roll Air Company
• Easy installation and setup
• Minimal need for repair and maintenance programs
• Minimal energy consumption and noise generation
• Environmentally friendly in terms of using R134a, R410a, and R404a refrigerant gases to prevent damage to the ozone layer.
• Equipped with a system to prevent freezing in low working capacities
• Equipped with a high-efficiency water separator to completely drain condensate and provide the driest air
• Equipped with a condensate drain system that prevents loss of compressed air when draining condensate
• Using heat exchangers with high efficiency that significantly reduces energy consumption
• Cabinets and internal electrical wiring with high reliability and safety coefficients
• Designed for reliable performance in harsh working conditions, including environment temperatures and high intake air temperatures
• Using quality elements and parts, including converters, compressors, refrigerants, valves, and electrical and electronic devices.
• Low internal pressure drop
• Suppose a refrigeration dryer has a high internal pressure drop. In that case, the compressed air compressor must consume more energy to compensate for this pressure drop, which causes energy waste and increases operating costs.
• Selecting and using dryers with high-pressure drops significantly leads to indirect energy costs.