Abstract: A method is described for recovering olefins by condensation from the reaction effluent stream from a cracking furnace containing olefins and hydrogen wherein a membrane separator is employed to reject the hydrogen from the reaction effluent stream. In such a manner, the dew point temperature of the stream can be increased and the energy required to provide refrigeration for olefin condensation can be reduced. The method comprises primary condensation, vapor-liquid separation and membrane hydrogen rejection steps followed by a series of cascaded chilling and vapor-liquid separation steps. Condensate recovered is processed in a demethanizer to separate light end components. Also disclosed is an olefins plant employing a membrane separator for rejecting hydrogen to enhance the energy efficiency and/or facilitate the expansion of plant capacity.

Abstract: A method for pretreating a natural gas stream using a single scrub column to remove freezable C.sub.5+ components and provide an LNG product which can be conveniently handled and shipped is disclosed. The method comprises feeding a natural gas stream to a feed point on a scrub column operated substantially as an absorption column wherein the heavy components are absorbed from the feed gas using a liquid reflux essentially free of such C.sub.5+ components. The feed can be vapor introduced at a low point on the column, or can be optionally split, cooled and/or expanded and introduced at one or more feed points on the column. The reflux stream can be overhead vapor condensate having a temperature of about - 40.degree. C., or methane-rich LNG or a combination of LNG and vapor condensate.

Abstract: Dilution steam for steam cracking hydrocarbons to produce lower olefins is economically provided by saturating gaseous hydrocarbon feed with water at a temperature selected to achieve the particular steam to hydrocarbon ratio desired in the steam cracking step. Complete saturation of the feed gas is ensured by injecting the gas into the flooded portion of an indirectly heated tubular saturation zone.

Abstract: Combustion air for steam cracking furnaces is preheated by indirect heat exchange with medium pressure and low pressure steam that has been expanded through steam turbines from high pressure steam produced in the hot section of an ethylene production plant.

Abstract: Hydrocarbon feed to a steam cracking furnace is heated to near cracking temperature by indirect heat exchange with steam to permit use of a range of feedstocks.