Process and plant for substitute natural gas

Abstract

A methanation section for producing substitute natural gas (SNG) by reacting a fresh syngas, the methanation section comprising adiabatic reactors connected in series, with heat removal and reacted gas-recirculation, wherein the fresh syngas is fed in parallel to said adiabatic reactors. In a preferred embodiment the reacted gas is recirculated to the first reactor and further dilution of the fresh gas at the inlet of the first and second reactor is achieved by steam addition.

1 . A methanation section for converting a syngas containing carbon oxides and hydrogen into substitute natural gas SNG, said methanation section comprising:
 a first adiabatic reactor, and a plurality of further adiabatic reactors, said reactors adapted to carry out a methanation reaction for producing SNG from a fresh syngas feedstock, said reactors connected in series such that each of said further reactors is fed with a gas stream taken from the previous reactor;   a fresh syngas feeding line arranged to feed in steady state operation said fresh syngas feedstock in parallel to said first and further adiabatic reactors, each reactor receiving a predetermined portion of the fresh syngas feedstock; and   a re-circulation loop receiving in steady state operation a portion of reacted gas taken from the first adiabatic reactor and mixing said portion of reacted gas with a fresh syngas feeding portion of the first adiabatic reactor, wherein said gas recirculation loop involved said first adiabatic reactor only.   
     
     
         2 . The methanation section according to  claim 1 , further comprising steam addition lines to further dilute the gas entering the first adiabatic reactor and a second further adiabatic reactor of the methanation section. 
     
     
         3 . The methanation section according to  claim 1 , comprising four reactors, said first adiabatic reactor and three of said further adiabatic reactors, wherein the fresh syngas feedstock is split 25% to the first reactor, 20% to the second reactor, 25% to the third reactor and 30% to the fourth reactor. 
     
     
         4 . The methanation section according to  claim 1 , wherein the reactors are adiabatic axial-flow or axial-radial flow reactors.