Method for transportation of low molecular weight hydrocarbons

Abstract

A system achieving a high density of transported natural gas by compressing it to high pressures typically above 5 MPa to transport the gas in a modified composition that permits a very low compressibility factor at near ambient temperature either above or below. This reduces greatly the size of the cooling systems that are required. In some cases cooling of the compressed gas may be achieved in a simple heat exchanger cooled by air or water. The transport of the gas takes place in self propelled ships or non-self propelled barges fitted with a cargo containment system capable of storing the cargo at high pressures, typically above 5 MPa and usually not above 25 MPa. The transport vessel may carry a store of higher molecular weight gases (c2 through c7) that when mixed with the incoming cargo results in a molecular weight of the mixture of at least 22 and possibly as high as 28 or higher. The store of higher molecular weight cargo may be gained from gases that condense during discharge of the vessel at its destination due to the adiabatic cooling of the cargo during discharge. These liquids may be retained aboard and transported back to the origin. If insufficient quantities of heavy gases are available at the origin they may be loaded at the destination. If required, the composition of the heavy gases transported back to the origin may be changed through partial discharge or partial receipt of additional hydrocarbons or a combination thereof at the destination point.