It looks like a coke drum.
In a delayed coker, which produces petroleum coke, the reaction occurs in the heater and on the way to the drum, where the coke settles out and the light hydrocarbon vapors go out the top. Here, top is to the left as the drum is positioned on the flatcar. The drum gradually fills with coke over an approximately 18-hour cycle, then when it's filled there's a switch valve that sends the stream of coke into another drum without stopping the flow. Then the fun begins. The drum is deheaded (opening the bottom "head") and high-pressure lances are used from the top to break up the 900 degree coke and send it out the bottom into a chute to the coke pile, where it becomes hopper car loads en route to coke users. Once the drum is empty, it's kept warn until its turn comes to be re-filled.
Driving past a refinery, the coker unit is distinctive and plainly visible as two or three of these drums high up in a structure, with what looks like a drilling rig on top. That's the structure that supports the process of lancing the coke. The only nozzles on the drum, other than the vapor flow out near the top, are those small thermowell nozzles which are mounted at an angle along the drum to detect the temperatures inside the drum as it's filled. The supports for the drum are at the top of the conical section, which is at the deheading deck level, sometimes called the tabletop. In the steam era, the deheading was an extremely dirty and dangerous job.
Perhaps more than you wanted to know.