Process for hydrotreatment of a fuel gas stream containing more than 4% olefins

Abstract

A process for the hydrotreatment of a fuel gas stream containing up to 15% olefins comprises the steps of introducing the fuel gas stream into at least one co-current reactor, where the stream is split into two flow fractions, of which one fraction is routed through an olefin treatment section, while the other fraction is routed through another section, subjecting the sections to heat exchange, combining the two flows, thereby equalizing temperatures and compositions, cooling the combined flow over a heat exchanger and reacting the combined flow to equilibrium in an adiabatic hydrotreatment reactor. A second co-current reactor with intercooling arranged in series after the first cocurrent reactor and before the final adiabatic reactor is used if the fuel gas stream contains more than 8% olefins.

Claims

1. A process for the hydrotreatment of a fuel gas stream containing up to 15% olefins, comprising the steps of: introducing the fuel gas stream into at least one co-current reactor, where the stream is split into two flow fractions, of which one fraction is routed through reactor sections containing catalysts active in olefin treatment, whereby the olefins are saturated to alkanes by hydrogenation, while the other fraction is routed through other reactor sections containing no active catalysts, subjecting the sections of active catalysts and the sections without active catalysts to heat exchange through pipe walls, metal sheeting or other forms of separation of the two section types, combining the two flows, thereby equalizing temperatures and compositions, cooling the combined flow over a heat exchanger, and finally reacting the combined flow to equilibrium in an adiabatic hydrotreatment reactor.

2. Process according to claim 1, wherein the fuel gas stream contains more than 8% olefins, requiring a second co-current reactor with an intercooler arranged in series after the first co-current reactor and before the final adiabatic reactor.

3. Process according to claim 2, wherein the intercooler between individual reactors is replaced by a quench stream.

4. Process according to claim 3, wherein cold feed gas is used as quench stream.

5. Process according to claim 3, wherein the quench stream comprises one or more of hydrogen, water, carbon dioxide and nitrogen.

Description

(1) The present invention is based on the idea of using a co-current reactor system, for instance the one described by the Applicant in WO 2012/172065 A1, for hydrotreating refinery fuel gases with an olefin level of 4 to 15%.

(2) More particularly, Applicant's WO 2012/172065 describes a method and a reactor for performing exothermic catalytic reactions. The method comprises the steps of providing a feed gas stream comprising reactants for the exothermic catalytic reaction to a fixed-bed catalytic reactor. The reactor comprises one or more catalytic beds, each having sections filled with catalyst particles, and a feed gas bypass provided inside the reactor by arranging a number of bypass passageways having a cooling area without catalytically active particles within at least one of the catalyst beds. A part of the feed gas stream is passed through the bypass passageways, and the rest of the feed gas stream is passed through the sections filled with catalyst particles. The heat is removed from the feed gas stream, which is passed through the sections filled with catalyst particles, by indirect heat transfer to the feed gas stream being passed through the bypass passageways.

(3) Specifically, the present invention concerns a process for the hydrotreatment of a fuel gas stream containing up to 15% olefins, comprising the steps of: introducing the fuel gas stream into at least one co-current reactor, where the stream is split into two flow fractions, of which one fraction is routed through reactor sections containing catalysts active in olefin treatment, whereby the olefins are saturated to alkanes by hydrogenation, while the other fraction is routed through other reactor sections containing no active catalysts, subjecting the sections of active catalysts and the sections without active catalysts to heat exchange through pipe walls, metal sheeting or other forms of separation of the two section types, combining the two flows, thereby equalizing temperatures and compositions, cooling the combined flow over a heat exchanger, and finally reacting the combined flow to equilibrium in an adiabatic hydrotreatment reactor.

(4) By heat exchanging through pipe walls, metal sheeting or other forms of separation of the two section types, the temperature increase will be significantly lower than it would have been in an adiabatic reactor.

(5) If the fuel gas stream contains more than 8% olefins, a second co-current reactor with intercooling will be required. This second co-current reactor is arranged in series after the first co-current reactor and before the final adiabatic reactor.

(6) Cooling between the reactors can be achieved by an intercooler with e.g. water, air or oil, separated from the product gas.

(7) The intercooler between individual reactors can be replaced by a quench stream of water or gases. In principle, quenching between reactors can be achieved with water or any gas, e.g. hydrogen, carbon dioxide and/or nitrogen. Cold feed gas can also be used as quench gas, and this is a preferred option.

(8) In one embodiment of the invention, with olefin levels of approximately 5-10%, a co-current reactor is designed and adjusted to hydrotreat only a portion of the feed gas olefins, as some of the feed gas passes through sections without active catalyst. The unreacted feed gas flows in parallel (i.e. co-current) to the reacted gas and exchanges heat with the reacted gas through a metal wall, which typically is a pipe or a flat surface. This way, the temperature of the reacted gas is reduced.

(9) After the reactor, the reacted and the unreacted streams are combined, cooled and routed through a final adiabatic reactor. At this stage, full conversion to equilibrium has taken place, and the completely reacted product can be transferred to downstream units.

(10) In another embodiment of the invention, with olefin levels of approximately 10-15%, a secondary co-current reactor is inserted after the first co-current reactor, such that the complete unit consists of two co-current reactors and one adiabatic reactor, with cooling inserted between the reactors.

(11) The present once-through reactor solution to hydrotreatment of highly olefinic refinery fuel gas streams, which is both technically novel and innovative, presents very significant advantages in CAPEX. Thus, compared to a recycle system, there is no need for a recycle compressor, valves, pipes and control system, and the main reactors, valves and pipes can be smaller, since they do not need to carry the recycle flow.

(12) Also from an OPEX perspective, the advantages are significant. The often substantial electric power needed for the compressor is eliminated, and so is maintenance of the recycle compressor and system, i.e. valves and pipes. The hydrotreatment catalyst cost will also be reduced, as the lifetime-influencing flow is reduced.