a fuel conditioning process and apparatus for use where natural gas is compressed by a field compressor driven by a natural gas powered engine . the fuel portion of the compressed raw natural gas is passed through an adsorption vessel containing an adsorbent material capable of adsorbing impurities . the outlet gas from the adsorption vessel is accumulated and mixed for averaging and controlling the heating value of the outlet gas used for fuel . regeneration of the adsorption material , when employing multiple adsorption vessels , is accomplished by connecting one adsorption vessel to the suction side of the compressor , purified gas from another adsorption vessel in adsorption service is backflowed through the loaded adsorption vessel to desorb the previously adsorbed impurities , the flow of the compressed raw natural gas to the other adsorption vessel is terminated and the pressure within the two adsorption vessels is equalized . the regenerated adsorption vessel is then repressured with the compressed raw natural gas prior to returning it to the adsorption mode .