Process for the production of synthesis gas
The invention relates to a process for the production of liquid hydrocarbons by Fischer-Tropsch synthesis in which the reforming section of the plant comprises a process line comprising autothermal reforming (ATR) ( 5 ) or catalytic partial oxidation (CPO), and a separate process line comprising steam methane reforming (SMR) ( 8 ).
1. A process for the production of synthesis gas comprising:
(a) passing a first hydrocarbon feedstock, a tail gas from a Fischer-Tropsch (FT) synthesis stage, and an oxidant gas to an autothermal reforming (ATR) stage or catalytic partial oxidation (CPO) stage to form a raw synthesis gas;
(b) passing a second hydrocarbon feedstock through a primary reforming stage in the form of steam methane reforming (SMR), to form a primary reformed gas;
(c) combining part or all of the primary reformed gas of step (b) with the raw synthesis gas of step (a) to form a synthesis gas according to a R SMR ratio between 1 and 20%, where R SMR is defined as the volumetric flow rate of carbon monoxide and hydrogen in the primary reformed gas to the volumetric flow rate of the hydrogen and carbon monoxide in the synthesis gas.
2. The process according to claim 1 in which said first hydrocarbon feedstock and said second hydrocarbon feedstock are split from a single hydrocarbon feedstock and wherein prior to split the single hydrocarbon feedstock is subjected to pre-reforming.
3. The process according to claim 1 wherein naphtha formed or synthesised in the FT-synthesis stage is not added to the first hydrocarbon feedstock or the second hydrocarbon feedstock or to the single hydrocarbon feedstock.
4. The process according to claim 1 wherein each individual stream in the form of first hydrocarbon feedstock, or second hydrocarbon feedstock, or both, are subjected to pre-reforming prior to passing through autothermal reforming stage or primary reforming stage.
5. The process according to claim 1 further comprising subjecting primary reformed gas to the sequential stages of water gas shifting, separating a hydrogen-rich stream in a separation means, and mixing all or a portion of the hydrogen-rich stream with the produced synthesis gas of step (c).
6. The process according to claim 1 wherein the produced synthesis gas of step (c) has a molar ratio of hydrogen to carbon monoxide of 1.7-2.3.
7. The process according to claim 1 wherein in step (a) the autothermal reforming (ATR) stage is combined with heat exchange reforming (HER) arranged in series or in parallel.
8. The process according to claim 1 wherein the process further comprises previous to steps (a) or (b) a step of passing the first or second hydrocarbon feedstock through a desulfurization stage.
9. The process according to claim 1 wherein the process steam-to-carbon molar ratio (S/C) in step (a) is in the range 0.4-1.0, while the process steam-to-carbon molar ratio in step (b) is in the range 1.5-4.0.
10. The process according to claim 1 wherein the process further comprises subjecting primary reformed gas to the sequential stages of water gas shifting, separating a hydrogen-rich stream in a separation means, and mixing all or a portion of the hydrogen-rich stream with the raw synthesis gas of step (a).
11. The process according to claim 1 wherein the process further comprises converting the synthesis gas to liquid hydrocarbons by Fischer-Tropsch synthesis.