Two stage entrained gasification system and process
View Patent ↗The present invention relates to a system and process for gasifying feedstock such as carbonaceous materials. The invention includes partial combustion of dry solids and pyrolysis of carbonaceous material slurry in two separate reactor sections and produce mixture products comprising synthesis gas. The invention employs one or more catalytic or sorbent bed for removing tar from the synthesis gas. The inventive system and process allow a gasification to be carried out under higher slurry feeding rate and lower temperature with the provision to manage the tar being produced, therefore to increase the conversion efficiency of the overall gasification.
1. A process for gasification of a carbonaceous material, comprising the steps of:
a. introducing recycled char into a reactor lower section and partially combusting said recycled char therein with a stream comprising an oxygen-containing gas or steam thereby evolving heat and forming mixture products comprising synthesis gas and molten slag, wherein said reactor lower section is operated in a range of 2400° F. to 3000° F. and in a range of 150 psig to 1200 psig, wherein recycled char and said stream are introduced to said reactor lower section through one or more dispersion devices on said reactor lower section at a feed rate between 30 to 60 feet per second, and a residence time of said recycled char in said reactor lower section of 4 to 6 seconds;
b. passing said synthesis gas from said reactor lower section upward into a reactor upper section and pyrolysing therein with a stream comprising a slurry of particulate carbonaceous material in a liquid carrier, thereby forming mixture products comprising i) a gaseous product stream comprising synthesis gas and residual tar, ii) char, and iii) vapor, wherein said reactor upper section is operated in a range of 550° F. to 1300° F., and in a range of 150 psig to 1200 psig, wherein said slurry of particulate carbonaceous material in said liquid carrier is introduced to said reactor upper section through one or more feed devices on said reactor upper section at a feed rate between 20 to 60 feet per second, and wherein said slurry has a residence time in said reactor upper section of 5 to 40 seconds;
c. passing said mixture products from said reactor upper section through a separation device, wherein said char is separated from said mixture products from said reactor upper section and introduced to said reactor lower section as said recycled char of step a), wherein said recycled char is dry and is the only feedstock introduced to said reactor lower section; and
d. introducing said gaseous product stream from said reactor upper section comprising synthesis gas and residual tar into one or more catalytic beds comprising one or more catalysts selected from the group consisting of zeolite, supported nickel, limestone, and mixtures thereof, wherein said catalytic bed is operated between 1200° F. and 1600° F. and between 150 psig and 1200 psig, wherein said residual tar is decomposed, wherein said heat evolved in said step (a) is recovered by converting said slurry of particulate carbonaceous material and said carrier liquid in step (b) into said gaseous product stream in step (b).