All-Welded System Gauges Saves Downtime at Hydrogen Plant

Challenge

A hydrogen production plant was having to replace gauges every 30 days and needed a better solution. The facility’s operations can be basically characterized by the following processes; feed compression & preheating, feed desulfurization by hydrogenation, hydrogen production by steam-hydrocarbon reforming process, CO conversion by medium temperature shift reaction and hydrogen purification by pressure-swing adsorption (PSA). In addition to steam, feedstock to the hydrogen plant can include natural gas, pentane, refinery fuel gas, and ammonia. The fuel to the heater (reformer) is composed primarily of PSA off-gas. The balance of the fuel is either refinery fuel gas or natural gas. The hydrogen product is sold and delivered to the refinery along with a portion of the steam produced at the plant. The refinery provides this hydrogen plant with ammonia, pentane, refinery fuel gas, and certain utilities including treated water for steam production.

Solution

Valin’s technical specialists recommended an all-welded system gauge and installed it shortly thereafter. The application was on a pressure-swing adsorption process (PSA). The PSA runs through a process cycle every 15 minutes 4 times per hour, 24 hours a day. The gauge is moving either up or down the pressure scale in every minute, 365 days a year, in which the unit steps-up from 10 psi in increments of approximately 10 psi until it reaches 410psi and then decreases in pressure from 410 psi to 10 psi. The skid runs continuously for 3 years before a maintenance cycle is required.

Customer Benefits

Valin visited the customer sometime later and inquired after gauge replacement. They still had the original gauges that Valin replaced in 2009! The chart below shows the number of cycles these gauges have been through with estimates of 72 months of service. The refinery’s I&E Tech provided a tour to see the gauges and supplied Valin with several pictures to validate the information. Valin surveyed gauges for each application and assembled a spreadsheet of the process information for use when they purchase gauges for the remainder of the applications. The special gauge can be used in many applications where vibration and temperature are a challenge and the customer has experienced on-going gauge failures. The gauge is well-suited for applications in refineries, chemical, power generation and all other critical process applications.

The major design features of the All Welded System:

Upper and lower half of diaphragm body are welded together using a body construction weld.

Benefit: No bolts to potentially loosen in vibration and thermal cycling applications.

After gauge is threaded into the seal housing the threads are back-welded.

Benefit: Thread contact changes are fully resistant to thermal cycling, vibration and leaks caused by installers using the gauge case to orient the instrument. The back weld insures integrity is always maintained between instrument and seal. The potential loss of system fill fluid through the threads is eliminated.

The threaded diaphragm seal fill port is not present in this special gauge. Instead, a hole is drilled into the back of the gauge socket and it is used as a fill port. A pin is pressed into the drill hole and then it is welded closed.

Benefit: Ensures a tamper resistant and leak-proof design.

The all-welded gauge is lighter than bolted design diaphragm seals.

Benefit: This allows the use of male pipe threads and for retrofit of direct mount gauges.

As required, standard or high impulse capillary restrictors for pump discharge applications can be installed in the upside of the diaphragm.

Benefit: Restrictors will not clog because they are not located in the process. The result is an instrument that is stable and easy to read during pump cycling. Note: Liquid filling the case can dramatically enhance instrument life in pump discharge applications.

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