Process for producing synthesis gas

A process for producing a synthesis gas wherein a desulfurized light natural gas and steam are pre-heated and then a reforming reaction for the synthesis gas is carried out in two steps of a first step under adiabatic conditions and a second step under heating to produce the synthesis gas, said process comprising:

• a step of feeding the pre-heated desulfurized light natural gas and steam to a first step reformer to carry out a first step reforming reaction at a temperature of 500 to 750° C., and
• a step of introducing the reformed gas coming from the first step reformer into reformer tubes in a heating furnace (a second step reformer) to carry out a second step reforming reaction,
• wherein the first step reformer is filled with a catalyst in which nickel is contained in an amount of 3 to 20% by weight in terms of nickel oxide to the total weight of the catalyst or a platinum group metal is contained as a platinum group element in an amount of 0.2 to 5% by weight to the total weight of the catalyst in a carrier composed of CaO and Al2O3 and containing CaO in an amount of 0.5 to 25% by weight to the total weight of the catalyst, at least part of CaO forming a compound with Al2O3, and in which a porosity X of pores having a pore diameter of 0.5 μm to 20 μm is 0.08 or more, a porosity Y of pores having a pore diameter of less than 0.5 μm is 0.15 or more, and a porosity Z of the total pores is from 0.23 to 0.8 (provided that Z≧X+Y), or a catalyst comprising nickel as an active component in an amount of 3 to 20% by weight in terms of nickel oxide to the total weight of the catalyst in an α-alumina carrier containing 98% by weight or more of aluminum oxide, in which carrier a volume of pores having a pore diameter within a range of 0.1 to 0.5 μm is 0.2 cm3/g or more and a volume of pores having a pore diameter of 0.5 μm or more is 0.05 cm3/g or more.