NOVELTY - The method involves removing a first portion of a constituent of a gas stream from a first portion of the stream by adsorbing the constituent portion to a first adsorbent, and transferring heat from a second adsorbent to the first adsorbent to heat and partially purge the first adsorbent. A second portion of the constituent is removed from a second portion of the gas stream by adsorbing the second constituent portion to the second adsorbent, and heat is transferred from a third adsorbent to the second adsorbent to heat and partially purge the second adsorbent and cool the third adsorbent.    USE - Method for processing a methane gas stream obtained from sources for producing a low emissions vehicle fuel e.g. compressed natural gas (CNG) and liquid natural gas (LNG), for a vehicle e.g. light duty vehicle and heavy duty vehicle. Uses include but are not limited to farms, solid waste dumps, agricultural waste anaerobic digesters, landfills, smaller refineries and gas fields, and municipal sewage treatment plants.    ADVANTAGE - The method enables retaining sensible heat difference between the hot and cool adsorbents when the adsorbent is subsequently cooled, so that the purifying capacity of the adsorbent is increased per unit time, thus reducing capital cost and operating cost in distributed-scale purifier systems, and hence producing purified methane process streams at a relatively low flow rate. The method allows the adsorbent to be cooled to cryogenic temperatures and/or the process gas to be pressurized to 350-400 pounds per square inch absolute (psia) or 1000 psia, so as to reduce the cooling load on the refrigerator, thus improving effectiveness or adsorptivity of the adsorbent at low temperature. The method allows the heat exchange fluid to undergo a phase change as the heat exchange fluid is heated and cooled during thermal contact with the adsorbent in the vessels, so that two-phase heat exchange operation can increase overall efficiency of the system. The method enables achieving up to 98-99 percent methane retention efficiency, reducing cost of purifying a process gas with high concentrations of contaminants to levels required for production of LNG, thus reducing cost by an enough margin to allow economical operation at relatively small throughput values.    DETAILED DESCRIPTION - The constituent is contaminant. The adsorbents are natural or synthetic zeolite selected for high carbon dioxide adsorption and very low methane adsorption.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of a gas stream processing system.    Bulk purifier (102)    Post-purifier (104)    Refrigerator (106)    Controller (107)    Outlet (109)