Application Overview
High-pressure separator letdown valves are among the most severe control valve applications in a refinery and are found in the Hydrocracker and Hydrotreater units. The hot high-pressure separator (HHPS) and cold high-pressure separator (CHPS) each have two letdown valves that maintain separator level to ensure proper separation of liquid and gas products. Because of the multiple constituents involved along with the entrained gases and catalyst, these valves are exposed to a number of challenges:
- Outgassing
- Flashing
- Cavitation
- Vibration
- Entrained catalyst
- Corrosive H2S
The negative consequences of these phenomena, including erosion, excessive vibration, and noise, makes sizing and selecting valves especially difficult.
Types of Separators
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Hot High-Pressure Separators (HHPS)
The hot high-pressure separator (HHPS) cuts the heavy and light reaction products and recovers the hydrogen flashed off during the letdown from the reactor. The heavy product liquid is sent to the fractionator, stripper, or a combination of both. The light product liquid is cooled and injected with wash water to absorb ammonia (NH3) and hydrogen sulfide (H2S). The mixture is further cooled before entering the cold high-pressure separator by the recycle gas exchanger and fin fan (HHP separator cooler).
Separator Letdown Control Valve Solutions
Severe Service Valve Solutions
Emerson has specific Fisher™ sizing and engineered solutions for all separator letdown applications. These solutions are designed to address outgassing and flashing effects that can occur in more HHPS letdown valves and CHPS letdown valves. They offer protection against cavitation, erosion, plugging, and leakage.