HOC(HEAT OF COMPRESSION) DRYER

HEAT OF COMPRESSION TYPE DRYER

http://www.beko-technologies.com/fileadmin/02_Produkte/02_03_Trocknung/02_03_06_Everdry/02_03_06_06_Everdry_HOC-P/hoc_p_function_en.pdf
THEORY OF OPERATION
In HOC type dryer, hot air at 120 degree celcius to 140 degree celcius from Compressor discharge is directly used for the desiccant regeneration. Running cost of this dryer is virtually NIL. It has two drying towers filled with the Activated alumina or Molecular sieve desiccant and they alternate in process every 4-hour automatically.
Compressed air directly from air compressor discharge is taken to air dryer inlet through pipelines at 130 degree celcius (Min) temperature. This hot air is passed one drying vessel where saturated desiccant is regenerated by this high temperature air. After picking up moisture from bed, this air is cooled in an intermediate cooler. Here moisture is condensed and removed by an auto drain trap. At 40 degree celcius temperature this air passes through second drying vessel where moisture gets adsorbed ands dry air comes out. Cycle time is 4-hours regeneration and 4-hours drying. After 4-hours changeover of vessels takes place. In the regeneration cycle heating of the bed is only for 2-hours and thereafter the bed is cooled by dry air. Dry air is cooled to 40 degree celcius temperature before going out of the air dryer.
Due to NIL operating cost, this design is becoming more popular. To utilize full heat energy of compressor discharge, HOC type dryer should be located very close to compressor discharge. These dryers are recommended only for Dew-Point (-) 40 degree celcius and the capacities above 300 Nm3 /hr. In smaller capacity the hot air discharge does not reach 140 degree celcius and hence this design can't be used. 

SALIENT FEATURES
1. No loss of compressed air in purge. It is a no purge loss design.
2. Maintenance is easy and simple as there are no heaters and no other moving parts except 4- way valves.
3. Fully automatic, continuous operation without any attention of operator.
4. Negligible operating cost. It neither requires electric power for regeneration nor there do any purge loss of compressed air. 
CAPACITIES OFFERED
300 NM3 / HR TO 5000 NM3 /HR



 Functional Description 
  
• Fully automatic for continuous operation 
• Desorption by utilizing the heat of compression in partial stream operation 
• Cooling by means of the partial stream of cold compressed air 
• No compressed air loss for regeneration 
• Flow beneficial butterfly valves for low pressure drop 


Functional Sequence 

The functional sequence for the HOC-R dryer type can generally be subdivided into three phases: 

 1. Adsorption / desorption 
 2. Adsorption / cooling 
 3. Adsorption / stand by 

The entire process takes place at operating pressure in the adsorption, desorption and in the cooling 
phase. Thereby, the accumulated compression heat of oil-free compressed air can be used for 
desorption. – ENERGY-SAVING - 


Adsorption B1 / Desorption B2 

The partial stream of hot compressed air coming from the compressor flows via the hot air-inlet, valve K1 
and the HK2 4/2-way valve (connection 3/2) into desiccant vessel B2, which is in the desorption phase. The 
humidity adsorbed from the desiccant evaporates. The vapour is supplied to the cooler by the compressed-air 
partial stream, via the HK1 4/2-way valve (connection 2/1) and valve K3. 

Here, the compressed air is cooled down to the required adsorption inlet temperature. The condensate 
produced during the cooling process will be drained from the compressed-air system via a downstream 
condensate separator. Subsequently, downstream of throttle valve KS1, the cooled desorption partial air 
stream flows into the cool air partial stream coming from the compressor. 

The partial air stream required for regeneration can be adjusted manually by means of throttle valve KS1. 

 Now the volume flow is again equivalent to the flow rate of the compressor. The complete compressed-air 
stream is supplied via the HK1 4/2-way valve (connection 3/4) to the vessel which is in the adsorption phase 
(B1). During this phase, the air flows bottom-up through the desiccant bed and the desiccant adsorbs the 
humidity. The dried compressed air flows via the HK2 4/2-way valve (connection 4/1) and the dryer outlet to 
the point of use. 

Due to the desorption process, the humidity content of the desiccant is reduced. Simultaneously, the 
temperature of the desorption air at the adsorber outlet (here B2) rises. The desorption process is terminated 
as soon as the required process temperature is reached. 


Adsorption B1 / Cooling B2 

In order to avoid temperature and dew point peaks after the change-over, the heat stored in the desiccant 
(after desorption) is transported by means of the cold partial air stream. 

The cold compressed-air partial stream from the compressor flows via valve K4 and the HK1 4/2-way valve 
(connection 1/2) into the heated desiccant vessel. 

While the flow passes through desiccant vessel B2, the cold compressed-air partial stream takes up 
(adsorbs) the stored heat. The compressed-air partial stream heated by the desiccant flows to the cooler and 
is cooled down to adsorption temperature. Subsequently, downstream of throttle valve KS1, the cooled -
down partial air flows into the cool air partial stream coming from the compressor. 

Now the volume flow is again equivalent to the flow rate of the compressor. The complete compressed air is 
supplied via the HK1 4/2-way valve (connection 3/4) to the desiccant vessel intended for adsorption (B1). 
During the adsorption phase, the air flows bottom-up through the desiccant bed and the humidity is 
adsorbed by the desiccant. 
The dried compressed air flows via the HK2 4/2-way valve (connection 4/1) and the dryer outlet to the point 
of use. 
http://www.beko-technologies.com/fileadmin/02_Produkte/02_03_Trocknung/02_03_06_Everdry/02_03_06_06_Everdry_HOC-P/hoc_p_1_small.jpg 
Adsorption B1 / Standby B2 

If the adsorption phase is controlled and terminated by a dew point-dependent control (optional), the duration 
of the standby phase depends on the load condition of the adsorption vessel (here B1). Only when the 
drying capacity of the desiccant is reached (increase of the pressure dew point) will the switch-over process 
be initialised. 
In the event that the plant is operated in the "time-dependent switch-over" mode, the switch-over process is 
initialised after the pre-set cycle time has ended. 


Switch-over Procedure 
After the standby phase is terminated, adsorption is switched-over to the regenerated vessel (here B2) by 
reversing the 4/2-way-valves HK1 and HK2 to the corresponding position. Now, vessel B1, saturated with 
moisture, is in the desorption phase, while adsorption vessel B2 takes over the drying of the compressed air. 


Overview of the functional Sequence 


 B1 B2 
 Adsorption Desorption 
 Adsorption Cooling 
 Cycle time 
 Adsorption Standby 
 Desorption Adsorption 
 Cooling Adsorption 
Total cycle time 
 Cycle time 
 Stand-by Adsorption 
Switch-over 

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