Method and apparatus for drying compressed gases

Abstract

Method and apparatus for drying compressed air, comprising an adsorption dryer ( 300 ) situated downstream of a refrigeration-based dryer ( 100 ), wherein the refrigeration-based dryer ( 100 ) comprises a heat-recovery arrangement ( 10 ), an evaporator ( 40 ) and an arrangement ( 80, 90 ) to separate and drain condensate, and wherein the adsorption dryer ( 300 ) comprises a first column ( 160 ) and a second column ( 170 ), which contain adsorbing material and which are connected via a conduit ( 18 ) with two calibrated orifices ( 188, 189 ) and a heater ( 275 ) therebetween, and where the columns are included in a circuit for the compressed air so as to alternately work in the adsorption mode and the regeneration mode, and in which the compressed air entering the dryer ( 300 ) is taken in cold from the condensate separator ( 80 ), and the air exiting the dryer ( 300 ) flows back into the heat-recovery arrangement ( 10 ).

1 . Hybrid apparatus for drying compressed air, comprising an adsorption dryer situated downstream of a refrigeration-based dryer, wherein the refrigeration-based dryer comprises a heat-recovery arrangement, an evaporator and a condensate separator arrangement to separate and drain condensate, and wherein the adsorption dryer comprises a first column and a second column, which each contain adsorbing material, and which are included in a circuit for the compressed air so as to alternately work in the adsorption mode and the regeneration mode, and in which the compressed air entering the dryer is taken in cold from the condensate separator arrangement after having caused to flow through an oil-removal filter, and the air exiting the dryer flows back into the heat-recovery arrangement after having caused to flow through a dust filter, said first column and said second column are connected via a conduit provided with at least one calibrated orifice associated to at least one heater, so as to reduce the flow-rate difference between the compressed-air streams flowing through the conduit during the heating and cooling phases of the adsorbing material, respectively. 
     
     
         2 . Hybrid apparatus for drying compressed air according to  claim 1 , wherein said first column ( 160 ) and said second column are connected via a conduit provided with two heaters, between which there is interposed a calibrated orifice. 
     
     
         3 . Hybrid apparatus for drying compressed air according to  claim 1 , wherein said first column and said second column are connected via a conduit provided with two calibrated orifices, between which there is interposed a heater. 
     
     
         4 . Hybrid apparatus for drying compressed air according to  claim 3 , wherein said two calibrated orifices have the same size. 
     
     
         5 . Hybrid apparatus for drying compressed air according to  claim 1 , wherein there are provided two temperature probes fitted inside the conduit to control the at least one heater. 
     
     
         6 . Hybrid apparatus for drying compressed air according to  claim 1 , comprising a valve group adapted to selectively supply the compressed air to the columns of the adsorption dryer, wherein there is provided at least one temperature probe in a series arrangement with a valve and a sound-deadening filter to control both heating and cooling of the adsorbing material in the columns based on the temperature of the air being exhausted outside during regeneration of the columns. 
     
     
         7 . Hybrid apparatus for drying compressed air according to  claim 6 , wherein there are provided two temperature probes situated in the lower portion of the columns, respectively. 
     
     
         8 . Method for drying compressed air with the use of a hybrid-type dryer comprising a refrigeration-based dryer that includes a heat-recovery arrangement and is situated upstream to an adsorption dryer, the latter comprising a first column and a second column, each containing adsorbing material and a heating element therebetween, wherein the compressed air exiting the adsorption dryer flows back into the heat-recovery arrangement of the refrigeration-based dryer, the method comprising the following steps that are carried out alternately in the two columns:
 (i) adsorbing the humidity from the compressed air by causing the compressed air to flow from the bottom upwards or from the top downwards in one of the columns until the desired dew point is reached;   (ii) depressurizing the other column;   (iii) heating—under expansion upstream to and/or downstream from the heating element—of the compressed air exiting the one column and being delivered into the other column in a direction opposite to the flow direction of the compressed air in the adsorption phase and there is let into the one column in the regeneration mode, a minimum amount of heat as just sufficient to de-absorb and discharge the amount of water adsorbed in the previous adsorption phase;   (iv) cooling of the adsorbing material down to temperature close to the temperature of the compressed air exiting an. air condenser of the dryer through the use of compressed air exiting the one column, which is caused to expand down to atmospheric pressure and is let into the other column, and there is let into the one column a flow of dry, expanded compressed air so as to cause an upper portion of the adsorbing material to cool down to the temperature value of the cold inlet air for such length of time as to allow a lower portion of the adsorbing material to cool down to a pre-set temperature; and   (v) pressurizing the other column up to the same pressure as the one column to allow for a repetition of the cycle.   
     
     
         9 . Method for drying compressed air according to  claim 8 , wherein the minimum amount of heat delivered in the heating phase into the column in the regeneration mode corresponds to a flow rate that amounts to approx. 4 to 6% of dry compressed air heated up to a temperature of approx. 130 to 200° C. that flows therethrough for a minimum time as sufficient to create such temperature profile inside the column that, at the end of the heating phase, the temperature in an upper portion of the column moves to the inlet temperature of the dry regeneration air, whereas the temperature in a lower enables the heating phase to be stopped when the lower temperature exceeds a pre-set value depending on the adsorbing material being used and the desired regeneration degree, between approx. 30° C. up to approx. 80° C. 
     
     
         10 . Method for drying compressed air according to  claim 8 , wherein the pressurizing phase of a column may continue for a much longer time than the minimum necessary so as to take advantage of the adsorption capacity of the other column that is working in the adsorption mode to as great as possible an extent.