Hydrogen Purge and FillLet’s not get blowed up.

Training by:Shadman the Wonderguy

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.

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.

Gas control system diagram

Gas control system diagram

H2Analyzer Rack

Flow indicator

Purity Analyzer

Pressure Gauge

Pressu

re Tra

nsmitter

Filter

Indic

ator

pane

l

Hydrogen Circulation

H2 circulation is driven by fan blades attached to the RotorTherefore flow depends on RPM and is negligible on the Turning Gear

Hydrogen Dryer

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

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.

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.

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.

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.

Did I say channel locks?

Yes, but that was under what NOT to do.

Get the Brass wrenches from the Shift Sup office.

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.

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

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.

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.

Pure Hydrogen

Lined up to vent

CO2 lined up to bottom header

CO2 Fills generator and purges out all the H2

CO2 lined up to bottom header

H2 Lined up to vent

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.

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.

Lined up to vent

Dry compressed air

Isolate CO2

Isolate CO2

Dry compressed air

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.