Continuous pressure letdown system

A continuous pressure letdown system having a dusty gas stream with solid particulates flowing through the system, wherein the system is connected to a hopper, the system comprising:

• a discharge line connected to the hopper;
• a valve for controlling introduction of the dusty gas stream with solid particulates into the discharge line;
• a cascade nozzle assembly positioned downstream of the discharge line for decreasing a pressure of the dusty gas stream;
• a purge ring connected between the discharge line and the cascade nozzle assembly;
• an inert gas supply connected to the purge ring for introducing an inert gas into the cascade nozzle assembly;
• an inert gas throttle for controlling a flow rate of the inert gas into the cascade nozzle assembly;
• and
• a filter connected downstream of the cascade nozzle assembly for separating the solid particulates from the dusty gas stream.

A method of continuously decreasing a pressure of a dusty gas stream flowing through a gasification system, the method comprising:

• passing the dusty gas stream through a length of discharge line;
• passing the dusty gas stream from the discharge line through a cascade nozzle assembly having a sequentially increasing diameter to incrementally decrease a pressure of the dusty gas stream over a distance;
• and
• adjusting flow rate of the dusty gas stream entering the cascade nozzle assembly.