NOVELTY - Supplying steam and hydrogen feedstock to primary process for producing synthesis gas involves combusting a fuel in a reformer containing catalyst of a secondary process to produce hot synthesis gas; cooling the hot synthesis gas to produce steam and cooled synthesis gas; supplying the steam to primary process; treating a portion of cooled synthesis gas to produce hydrogen feedstock; supplying the hydrogen feedstock to primary process.    USE - For supplying steam and hydrogen feedstock for producing synthesis gas (Claimed).    ADVANTAGE - The method does not require investment of capital in a start-up boiler and hydrogen generating unit that are not operated at full capacity at all times. Natural gas or other fuel is not wasted to keep a boiler operating at turned-down conditions to ensure that steam is available during plant upset conditions. The steam reformer can be rapidly switched from producing little export steam to maximum export steam and back to little export steam, as required.    DETAILED DESCRIPTION - Supplying steam and hydrogen feedstock to a primary process for producing synthesis gas involves in a reformer of a secondary process, (where the reformer comprises several catalyst containing reforming passages) combusting a fuel to provide heat and a hot combustion gas and using the heat to heat all of the reforming passages; producing a hot synthesis gas by catalytically endothermically reforming a hydrocarbonaceous gas in the presence of process steam in some of the catalyst containing reforming passages only; cooling the hot synthesis gas by heat exchange with water to produce steam and cooled synthesis gas; supplying the steam to the primary process for producing synthesis gas; treating at least a portion of the cooled synthesis gas to produce a hydrogen feedstock; supplying the hydrogen feedstock to the primary process for producing synthesis gas; cooling the reforming passages not producing hot synthesis gas by passing a cooling or heat transfer medium through the reforming passages; and separating the hot synthesis gas exiting some of the reforming passages from the cooling or heat transfer medium exiting other reforming passages so that the hot synthesis gas and the cooling or heat transfer medium do not mix.    INDEPENDENT CLAIMS are included for the following:    (1) starting a hydrocarbonaceous gas conversion plant (which has start-up hydrogen and steam requirements) involving: heating a reformer comprising several catalyst containing reforming passages passing through a heating zone by combusting a fuel to producing a hot combustion gas; generating steam by transferring heat generated by the combustion of the fuel to water in a steam generation circuit; producing hot synthesis gas from some of the reforming passages only by feeding a hydrocarbonaceous gas and at least some of the generated steam into the reforming passages; generating more steam by transferring heat from the hot synthesis gas to the water in the steam generation circuit; treating at least a portion of the synthesis gas to produce a hydrogen feedstock; and supplying at least a portion of steam and the hydrogen feedstock to the hydrocarbonaceous gas conversion plant to satisfy the start-up hydrogen requirements of the hydrocarbonaceous gas conversion plant; and    (2) an installation for producing steam and synthesis gas comprising a reformer which includes several catalyst containing reforming passages passing through a heating zone (where the reforming passages having inlets grouped into at least two groups and outlets grouped into at least two groups); a feed arrangement having a first condition in which a hydrocarbonaceous gas and steam can be fed into one group of inlets and a cooling or heat transfer medium only can be fed into another group of inlets, and a second condition in which a hydrocarbonaceous gas and steam can be fed into both of the groups of inlets; a discharge arrangement having a first condition in which synthesis gas can be removed from the group of outlets of the reforming passages fed with the hydrocarbonaceous gas and steam, and in which the cooling or heat transfer medium can be removed from the reforming passages fed with the cooling or heat transfer medium only, without mixing the synthesis gas and the cooling or heat transfer medium, and a second condition in which synthesis gas can be removed from both groups of outlets; and a waste heat boiler to generate steam by heat exchanger between the synthesis gas produced and boiler water.