This document provides instructions for purging hydrogen from a generator and filling it with hydrogen safely. It outlines that hydrogen must be purged using carbon dioxide then air due to its explosive properties. The process takes at least 4 hours and over 1,100 pounds of carbon dioxide to fully purge the hydrogen. Precise valve lineups and secondary checks are required when working with hydrogen to avoid explosions.

1. Hydrogen Purge and Fill
Let’s not get blowed up.
Training by:
Shadman the Wonderguy

2. Why Hydrogen?
• Hydrogen is the gas with the highest thermal
conductivity. (It heats and cools the fastest)
• H2 is also the lightest gas which minimizes
“windage losses” and friction heat
• If we cooled the turbine rotor with air instead
of H2, the rotor would have to be designed
with 7x as much surface area (and extra mass)
resulting in efficiency losses.

3. Did you say “blowed up”?
• At concentrations >4% H2 is flammable.
• At concentrations >18% H2 is explosive
• The Minimum Ignition Temperature of H2 is
1/10th that of gasoline.
• The loop-hole is it can only blow up in the
presence of oxygen.
• The Upper Explosive Limit is 75% purity in air.
If purity is above that the H2 is stable.

4. Gas control system diagram

5. Gas control system diagram
H2Analyzer Rack

6. Hydrogen Circulation
H2 circulation is driven by fan blades attached to the Rotor
Therefore flow depends on RPM and is negligible on the Turning Gear

7. Hydrogen Dryer

8. From Gen to Dryer
(Discharge side of fan)
From Dryer to Gen
(Suction side of fan)
Closed Cycle
Cooling Water
CO2 for purging
To Vent

9. Dryer Operation
• Dryer is full of Hydrogen and attached to Generator on
opposite sides of the rotor fan.
• One tower is in service and desiccate removes the
moisture from the H2. Dewpoint monitors on inlet and
outlet let you know it’s working
• The opposite tower is heated to remove the moisture
from the desiccate. It has a blower to move the H2
through a cooler.
• When the H2 is cooled below the dewpoint the moisture
condenses into the drain trap and is removed.

10. Normal make up to the generator
comes through a pressure regulator
and goes to a distribution header that
is physically at the top of the
generator.

11. Normal make up to the generator
comes through a pressure regulator
and goes to a distribution header that
is physically at the top of the
generator.

12. When H2 press on the truck drops
to a couple of hundred pounds
you will have to swap the hose to
the opposite truck.
Fittings are brass / non-sparking.
Brass fittings are reverse threaded to
ensure they are not mixed with steel
fittings.
Left-handed fittings are typically
marked with notches to notify the
operator, and hopefully prevent
him from gronking the wrong way
on them with channel locks.

13. Did I say channel locks?
Yes, but that was under what NOT to do.
Get the Brass wrenches from the Shift Sup office.

14. Before venting the generator
casing the unit must be offline
and the shaft stationary or on the
turning gear
Then secure the hydrogen make-up
and vent the pressure from the
casing from 75psi down to 7psi.

16. Normal line-up of the purity analyzer relies on the rotor fan for DP.
Therefore the meter reading is “stale” when the unit is offline.
During venting the line-up has to be changed

17. Normal line-up of the purity analyzer relies on the rotor fan for DP.
The meter reading is “stale” when the unit is offline.
Therefore during venting the line-up has to be changed
By throttling TGE-BV-118 to maintain pressure on the generator
you provide DP to force flow through the analyzer while venting.

18. Purge Hydrogen with CO2
• Hydrogen in the casing is vented down from
75 psi to ~5psi through the header at the top
of the generator.
• CO2 is lined up to the bottom header to push
the rest of the H2 out. Since CO2 is denser
than H2 the CO2 will fill all the pockets in the
gen driving the H2 out the top vent.
• Continue this until the purity meter reads <2%
H2 in CO2.

19. Pure Hydrogen
Lined up to vent
CO2 lined up to
bottom header
CO2 Fills generator and purges
out all the H2

20. CO2 lined up to
bottom header
H2 Lined up to vent

21. It will take at least 4 hours to purge out the
hydrogen.
Toshiba says you will have to purge 2.5x the
volume of the generator, which will take at
least 1,100 lb of CO2 from the storage tank.

22. And Finally : AIR
• The explosive danger has passed, but the
generator is still unsafe to enter.
• The final step is to push the CO2 out with dry,
breathable air from the instrument air header.

23. Lined up to vent
Dry compressed air
Isolate CO2

24. Isolate CO2
Dry compressed air

25. After work is complete
This training is a supplement to (NOT a
replacement of) OP301A.
Please follow the procedure precisely and
have all valve line-ups second checked.
Do it again Backwards
to safely charge the gen with H2.