system
Given the following post, respond as if you're commenting on Reddit:
human
In Canada, I often see train cars carrying "hot molten sulphur".  Why is it transported in liquid form instead of solid?
gpt
Former employee of a sulfuric acid plant here.

Most sulfur comes as a byproduct of petroleum refining.  At the refinery, the sulfur stream is already liquid, and the pumps are of mature designs that do a pretty good job of handling it.  The railcars are filled with this hot (300F +/-10) molten sulfur.  The cars are insulated to

A: help retain whatever heat it can and 

B: to protect whatever poor thing might bump into it.  

So this sulfur is usually is frozen solid by the time it gets where it is going.  The railcar has steam coils in it.  ~75psi steam will melt a railcar in about 12-18 hours depending on the weather.  Once there are no solid chunks, a valve on the bottom of the car is opened, and it dumps into a pit.  From there it is pumped to a storage tank, and then gravity fed into another pit.  This pit has high pressure pumps that spray it into a furnace to start the sulfuric acid production process.



TL;DR- the source produces molten sulfur, and the end user needs it in its molten state.