A combined dryer, in layman's terms, is a combination of a traditional cold dryer and a suction dryer.

In many occasions, the refrigeration dryer and the suction dryer are used alone, which cannot reach the pressure dew point required by the customer, resulting in liquid water in the compressed air, which is harmful to equipment and production.

So some people imagine whether it is possible to combine the refrigerated dryer and the suction dryer to complement each other's advantages.

The cold dryer can remove 80-95% of the moisture in the compressed air, but it cannot do deep drying; while the adsorption dryer, when dealing with large flow or encountering high temperature in summer, the drying effect will also be greatly affected.

If a cold dryer is used for pre-drying, then the suction dryer at the back end only needs to undertake less than 20% of the drying tasks. Even if it is working under high load, it can basically ensure that the air consumption at the back end meets the standard.

This is the fundamental reason why the combined dryer is widely used: the drying effect is good.

With the popularization and use, people gradually found that the combined dryer also has the advantages of convenient installation and space saving;

The original combined dryer is actually the air outlet at the rear end of the refrigerated dryer connected to the adsorption dryer, and then installed on the same base.

Is it possible to improve the drying effect of the equipment and reduce energy consumption by optimizing the combination method?

Dryer manufacturers have begun to develop various bold designs around this starting point, and there are two combinations that have been widely adopted by many manufacturers.

1. The low temperature air of the cold dryer is directly connected to the suction dryer

The low-temperature outlet gas of the cold dryer is directly sent to the adsorption tower of the suction dryer for adsorption treatment;

The original intention of this design is to improve the adsorption efficiency of the adsorbent, because the characteristics of the adsorbent are: the lower the temperature, the better the adsorption effect.

However, the feedback received by a large number of users on the spot is that the drying effect is unstable, and liquid water occasionally appears at the back end;

Through a large number of analysis and testing, it is concluded that the reason for this result is that the liquid water mist penetrates the adsorption tower, is not adsorbed by the adsorbent, and enters the back end of the gas consumption.

The liquid water mist can penetrate the adsorption tower without being adsorbed, mainly because the density of the water droplets is much greater than that of the compressed air, so the momentum obtained in the airflow is large, the penetrating force is strong, and it can repeatedly collide with the adsorbent and not completely. adsorption, and finally escape from the adsorption tower.

If the effect of the pre-filter is good, keeping the liquid water mist outside the suction dryer as completely as possible can actually solve this problem.

Of course, fundamentally, the design didn't have the desired effect.

2. The excess heat of the cold dryer is recycled for the regeneration of the adsorbent

There has also been a design in the industry that uses the heat generated by the compressor of the refrigeration dryer to heat the regeneration gas of the suction dryer to reduce the heating power of the suction dryer;

Later data showed that the heat generated by the compressor of the refrigerated dryer was not only low in temperature, but also less in heat, which could not meet the requirements of the regeneration of the suction dryer at all.

So this short-lived design quickly died.

It is emphasized here: to achieve a dew point of -70 degrees, the suction dryer must use molecular sieves, the regeneration temperature of molecular sieves must be greater than or equal to 180 degrees, and the heating time must be no less than 1.5 hours, otherwise molecular sieves cannot be effectively regenerated.

For the dew point requirement of -40 degrees, the alumina regeneration temperature should be at least higher than 80 degrees, and it is generally reasonable and safe to heat it to 120 degrees.

Finally, after experiencing all kinds of strange combinations in the industry, everyone came to a conclusion: it is still the best to use "uncombined combined dryers"!

Therefore, if the on-site working conditions permit, it is recommended to use the suction dryer and the cold dryer in series, which is more convenient in daily maintenance and post-maintenance work.

FROM:Karen Chen