22 | Valve MAGAZINE
BEYOND FOSSIL FUELS
add to this nation’s capacity. (The company also has leases in three other
areas in the Western U.S. in various
stages of development.)
Utility-scale geothermal energy production involves tapping volcanic heat
to create steam—either by capturing
existing steam, flashing superheated
water into steam or pumping water into
hot rock formations to produce steam
in situ. Pressures are frequently in the
vicinity of 5000 psi and temperatures
get up to about 800º F, says Dave
Clark, business development manager
for refining in the Valve & Measurement division of Cameron. This doesn’t
present much of a challenge for valves,
but corrosion and erosion do. What
comes out of the earth is generally far
from clean—the steam at the Larderello facility, for example, has heavy concentrations of boric and sulfuric acids,
and the plants in California’s Salton
Sea area must contend with salt.
“One of the hardest things to control
in metallurgy and valves is the pH factor
of water,” explains Clark. “If the pH
factor is off, it causes very severe corro-
sion.” Sometimes all wetted surfaces
must be inlaid with 625 Inconel for pro-
tection—in some cases, Clark continues,
“all the way out to the ring groove on the
flange.” This does a good job, according
to Byron Paris, product manager of gate
valves in the Valve & Measurement divi-
sion, Cameron, but it makes the valve
more difficult to manufacture, he says,
and more expensive. On the other hand,
“they’re really bullet-proof valves…
I went out and witnessed a few of them;
they took them out of the line [after four
or five years of service] and they were as
clean as a whistle.” WCC carbon steel
doesn’t last very long under these condi-
tions, he points out. “[We] took out a
couple of carbon steel valves where they
didn’t have that protection and there
Cameron makes a line of wellhead
assemblies (Figure 7), including equip-
ment for geothermal applications. Clark
says a simple slab gate valve is the best
choice for geothermal applications,
“because an expanding gate valve’s got
angles on the back sides of these gates,
and when corrosion gets back there and
starts doing a number on it, it can freeze
Figure 7.
Typical
geothermal
wellhead
assembly
PHOTO: CAMERON
up on you.”
Along with the corrosion, says Clark,
geothermal must deal with particulates,
“picking up rocks and sand and grit, and
the seating area of the valve is subject to
some pretty severe damage.” A 625 or
tungsten carbide inlay can help here as
well, and “if we put valves out in sandy
service, the customer usually asks for
Stellite 6,” says Paris.
A BRIGHT FUTURE
It’s hard to keep up with what’s happening in the field of alternative energy
today because it’s happening fairly rapidly. The world’s focus on trying to find
ways to create energy that don’t involve
oil or gas, coupled with individual countries’ desires to become more energy
independent mean developments aren’t
likely to slow anytime soon. Whatever
happens, though, we can be assured that
valves and actuators will be an important part of the picture. VM
PETER CLEAVELAND, a contributing editor to Valve
Magazine, writes extensively about issues related
to the flow control industry. Reach him at pcleaveland@earthlink.net.
