Feed ratio control for hter

A method for designing the construction of a Heat Exchange Reformer (HER) to minimise metal dusting, said HER being part of a synthesis gas production unit, said synthesis gas production unit comprising a Main Reforming Unit (MRU) and a Heat Exchange Reformer (HER), wherein the effluent from the MRU is arranged so as to provide heat to the HER, and wherein a hydrocarbon feedstock is arranged so as to pass in parallel through both the MRU and the HER, thus providing:

• a. an MRU hydrocarbon feed having an MRU steam-to-carbon ratio (MRUS/C), an effluent outlet temperature (TMRU) and a MRU hydrocarbon flow rate (FMRU) and
• b. an HER hydrocarbon feed having an HER steam-to-carbon ratio (HERS/C) and an HER hydrocarbon flow rate (FHER), said method comprising;
• determining how the temperature profile within the HER varies with the distance from the inlet of the HER as a function of the ratio of FHER/FMRU, the MRU outlet temperature (TMRU), the MRU steam-to-carbon ratio (MRUS/C), the HER steam-to-carbon ratio (HERS/C) and the total hydrocarbon flow rate (FMRU+FHER);
• from said temperature profile, determining a distance (A) from the inlet of the HER at which metal dusting is not significant;
• at a distance greater than said distance (A) from the inlet of the HER, constructing the HER from a first metal has a higher resistance to metal dusting;
• and
• at a distance less than said distance (A) from the inlet of the HER, constructing the HER from a second metal which has a lower resistance to metal dusting than said first metal.