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