Specification Requirements for a Control Valve for Slurry Letdown Service

摘要

The conditions for this valve were derived from the Gulf Science and Technology Company SRC-II process demonstration plant. The first valve (V1) must let down pressure from 2000 psi to 460 psi, a total delta P of 1540 psi, with the other valves (V2, V3, V4) each experiencing a lesser drop. It should be noted that temperatures throughout the pressure letdown system are, at the lowest, seven hundred and seventy-five degrees Fahrenheit, but with a possible maximum to eight hundred degrees Fahrenheit. Due to the carcinogenic nature of certain compounds in the coal slurry, the maintenance of valves in the field and under process run conditions is inadvisable. All maintenance will be performed during regularly scheduled annual turnaround periods, at which times all lines carrying slurry can be flushed with solvent and steam prior to opening up for maintenance. With the above constraints, it has been determined that letdown stations to each vessel will have a group of letdown valves in parallel. Each will have a tight shutoff block valve or valves upstream of the letdown valve. Thus, as a letdown valve becomes eroded to the point of uncontrollability, it may be isolated and the secondary valve put into service. (ERA citation 04:055970)