Method of treating or recovering gaseous hydrocarbon contained in waste gas

A method of treating or recovering a gaseous hydrocarbon contained in waste gas employing a pair of adsorption apparatus which alternately performs adsorption and desorption processes, in which the waste gas containing the gaseous hydrocarbon is passed through one of the adsorption apparatus so that the gaseous hydrocarbon is adsorbed by adsorbent layers, enabling the adsorption apparatus to release the treated waste gas containing substantially no gaseous hydrocarbon, while at the same time the other adsorption apparatus is switched to the desorption process, the gaseous hydrocarbon adsorbed by the adsorbent is drawn by a vacuum pump to separate the gaseous hydrocarbon from said adsorbent layers, and the gaseous hydrocarbon is recovered from separated outflow purge gas, said method being characterized in that:

• (1) double-cylinder or multi-cylinder adsorption apparatus, in which each adsorbent layer is indirectly cooled by cooling water, are employed as said adsorption apparatus;
• (2) each adsorbent layer is a packed layer of one or more kinds of materials selected from activated carbon, synthetic zeolites and hydrophobic silica gel;
• (3) swing time required for switching between the adsorption and desorption processes is set to 1 to 15 minutes, and
• (4) each adsorbent layer is evacuated under vacuum while being purged by using part of clean gas evacuated from each adsorbent layer and/or air in the desorption process;
• and
• (5) the gaseous hydrocarbon is recovered from the outflow purge gas, and as means for recovering the gaseous hydrocarbon from the waste gas which is used in the desorption process employing a combination of evacuation under vacuum and purging operation, the steps of:
• 1) causing the outflow purge gas of a completely dry vacuum pump which is employed as said vacuum pump to be discharged upon increasing its gas pressure to 10 atmospheres, exceeding the normal atmospheric pressure;
• and
• 2) increasing the density of the gaseous hydrocarbon contained in the outflow purge gas by using as a cooling medium of the vacuum pump a liquid hydrocarbon of the same properties as the gaseous hydrocarbon contained in the waste gas and returning resultant gaseous hydrocarbon to an outlet pipe of a desorption apparatus, or by injecting the liquid or gaseous hydrocarbon of the same properties into the adsorption apparatus upon completion of the adsorption process to purge the apparatus and evacuating it under vacuum;
• and then accelerating liquefaction of the gaseous hydrocarbon by cooling it, or accelerating recovery of the gaseous hydrocarbon by an absorption method.

A method of treating or recovering a gaseous hydrocarbon contained in waste gas employing a pair of adsorption apparatus which alternately performs adsorption and desorption processes, in which the waste gas containing the gaseous hydrocarbon is passed through one of the adsorption apparatus so that the gaseous hydrocarbon is adsorbed by adsorbent layers, enabling the adsorption apparatus to release the treated waste gas containing substantially no gaseous hydrocarbon, while at the same time the other adsorption apparatus is switched to the desorption process, the gaseous hydrocarbon adsorbed by the adsorbent is drawn by a vacuum pump to separate the gaseous hydrocarbon from said adsorbent layers, and the gaseous hydrocarbon is recovered from separated outflow purge gas, said method being characterized in that:

• (1) double-cylinder or multi-cylinder adsorption apparatus, in which each adsorbent layer is indirectly cooled by cooling water, are employed as said adsorption apparatus;
• (2) each adsorbent layer is a packed layer of one or more kinds of materials selected from activated carbon, synthetic zeolites and hydrophobic silica gel;
• (3) swing time required for switching between the adsorption and desorption processes is set to 1 to 15 minutes, and at least a specified amount of air is used when the state of reduced pressure created in the desorption process is returned to the normal atmospheric pressure when switching between the adsorption and desorption processes, and
• (4) each adsorbent layer is evacuated under vacuum while being purged by using part of clean gas evacuated from each adsorbent layer and/or air in the desorption process;
• and
• (5) the gaseous hydrocarbon is recovered from the outflow purge gas.