What are the requirements of medical compressed air for dryers

With the in-depth reform of the medical system and the continuous improvement of the life support system in the medical industry, medical compressed air has also become an important part of the modern medical system and is a life support system. Its importance has been highly valued, GB50751-2012 "Medical Gas Engineering Technical Specification" hereinafter referred to as the "Specification" has detailed regulations on the quality of compressed air.

For the design and application of medical compressed air systems but not every air compression equipment manufacturers are familiar with, depending on the design drawings of major hospitals in the medical industry to choose the matching, inevitably a variety of optional phenomena. This article mainly focuses on the characteristics of the medical compressed air system and the requirements of the "specification", the adsorption drying tower for the introduction.

For the air pressure system, the dryer generally has two choices: refrigerated dryer and adsorption desiccant dryer. Refrigerated dryers are not very suitable for medical compressed air systems due to their own design characteristics listed below.

One is that the pressure dew point can only reach 2 ℃ ~ 7 ℃; the second is that the operation of air-cooled refrigerated dryers have requirements for the ambient temperature, in the summer when the ambient temperature is high, the output air dew point reliability is not high; third when the system load is less than 30%, the freeze dryer's gas-water separator efficiency is very low, resulting in condensed liquid droplets with the air to reach the downstream system, causing the downstream dew point alarm, especially in the evening when the air volume is greatly reduced, the Specification" has clear provisions on the moisture content of air.

The selection of adsorption desiccant dryers to achieve reliable dew point and function requires consideration of several important factors, as follows:

Flow rate

The flow rate of the adsorption dryer is generally selected according to the actual average highest consumed air volume, and it can also be selected according to the air supply volume of the air compressor. What needs to be clarified here is that the adsorption dryer generally consumes 15% of the flow rate for regeneration of desiccant under 7 bar pressure system. These losses should be fully considered when designing the system.

Minimum working pressure

When the actual consumed air volume is larger than the air supply capacity of the compressor, the pressure of the compressed air system will decrease, which will cause the adsorption dryer to exceed the load and the output dew point is not reliable. There are two reasons for this; one is the low pressure, the volume flow rate becomes larger, and the compressed air will bring more "moisture" - water vapor. The second volume flow rate becomes large, causing the compressed air in the dryer flow rate is too fast, water vapor is not fully dry, thus affecting the drying effect. To prevent the dryer from overloading, you can set the flow rate control.

Inlet air temperature

The moisture content of compressed air has a great relationship with the inlet air temperature. The inlet air standard temperature of general adsorption dryer is 35℃. If the inlet air temperature becomes 50℃, the compressed air entering the dryer will carry more than double the water vapor content, which is much higher than the processing capacity of the dryer. The adsorption capacity will decrease, causing the dew point at the outlet to fall below -40°C.

The capacity of the adsorbent varies with temperature. The adsorption capacity of adsorbent decreases with the increase of temperature, and for alumina, when the temperature reaches 50℃, its adsorption capacity decreases greatly. Therefore, in general, the standard inlet air temperature for adsorption dryers is 35°C.

Energy saving

Small pressure loss: (1) modular design, uniform airflow distribution, uniform drying; (2) blizzard filling method, avoiding airflow impact causing desiccant wear, powder will further increase resistance and cause dust "pollution" in subsequent equipment; (3) built-in import and export filters, minimize the external filters and pipelines caused by resistance loss caused by external filters and pipelines.

When using dew point control instead of standard

Timing controller due to the influence of inlet air temperature and pressure, in the selection of models often choose a larger processing capacity of the dryer to ensure a reliable dew point, which will cause most cases, the actual flow does not reach the rated processing capacity, the drying cylinder is not fully utilized to switch regeneration, and regeneration has been continuous.

In fact, the upfront investment is only a very small part of the operating cost of the dryer over its entire life cycle. More of the investment is the operating cost of the equipment. With a 10Nm3/min system, if the average air consumption is only 50% (in the evening and most of the time the system utilization is actually below 30%), then the energy saved by using the air inlet temperature and dew point switching mode can reach at least 60%, and the electricity cost is wasted. With the dew point control mode, the drying cylinder will continue to work until the gas dew point is close to the control point before switching, while the regenerated gas will stop consuming regenerated gas and be in a waiting state after the regeneration is completed, which will greatly save the regeneration gas consumption during this period.

If a modular adsorption dryer can be designed, it has a smaller size, lighter weight, easier installation and handling, and almost no special handling tools are needed compared to the traditional double tower suction dryer. It is more suitable for medical industry which needs quiet and reliable life environment.

Can reduce the amount of equipment maintenance tasks. It can be filled with desiccant on site, and will not cause rapid powdering of desiccant, blocking silencer, causing energy waste, or even causing downstream air pollution and equipment blockage. This desiccant is beneficial for use in the medical industry for life system gas.

In terms of control and alarm system dryer, it has dew point control and alarm mode remote control function, which can be linked with hospital intelligent energy system for resistance-free control and management. Control function requirements are as follows: when the pressure dew point of the dryer is better than -42℃ pressure dew point, the dryer can supply gas and does not affect the system flow and pressure, the system will prompt the alarm and upload data to the intelligent management system. When the pressure dew point is higher than -40℃, the machine is in normal mode to ensure the dew point reaches -40℃. Under normal conditions, if the dew point of the dryer does not reach -30°C, there will be an alarm signal flashing at the panel and a remote alarm system will be activated to indicate the need for maintenance.

In summary, in the face of the increasing requirements for compressed air system air quality in the medical industry system, it is necessary to ensure that the compressed air always obtains a reliable dew point and system operation is stable. At the same time, energy-efficient and low-carbon operation is increasingly considering the wisdom of the design and management, and the need to consider the overall cost of the adsorption desiccant air dryer equipment.

Lingyu Machinery ~ low dew point regenerative desiccant compressed air dryer