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The Facts
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Questions and Answers are listed below.
Questions & Answers
Recent updates
 What is the difference between ACFM and SCFM? How are they calculated?
What is the lowest temperature at which Chloro-Cat units have continuously and successfully (at least 4 months) operated?
What is the operating temperature when oxidation is occurring at the site of the catalyst?
Are there provisions for cooling the components in warmer (plus 100°F) weather?
Frequently asked questions
What can you tell me about halogenated compounds?
What about sulfur-bearing compounds and the lead at gasoline sites? How do these contaminants affect oxidation technologies?
I've heard about carbon adsorption. How does oxidation compare?
People often use LEL, vapor concentration, and mass loading when dealing with an oxidation device. How are these terms interrelated and what do they mean?
What are the differences between regenerative blowers, positive displacement blowers and vacuum liquid ring pumps? Why should one be selected over another at a SVE site?
What are some other vapor treatment technologies?
What about treatment in densely populated or residential areas?
Is Global's system safe for bulk terminal sites?
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What is the difference between ACFM and SCFM? How are they calculated?
ACFM and SCFM are units for volumetric airflow rates.
ACFM = Actual Cubic Foot per Minute
SCFM = Standard Cubic Foot per Minute
ACFM is a measure of the actual volumetric air flow rate at the
conditions of the air stream. The density of air varies with temperature and pressure.
SCFM is a measure of the volumetric flow rate if the air stream were at
standard conditions. Standard conditions are defined as 70F and 1
atmosphere pressure.
For example:
Convert ACFM to SCFM
5,000 ACFM of air at 230F and 1 atm The ideal gas law tells us the relationship between air temperature and air
density is directly proportional. Therefore we can convert ACFM to SCFM
using the temperature ratio (absolute temperature).
SCFM =
ACFM * (standard condition absolute temperature) / (actual absolute temperature)
SCFM =
5,000 * (70 + 460) / (230 + 460) 5,000 ACFM of air at 230°F
and 1 atm = 3,841 SCFM.
The equation can be rearranged to convert SCFM to ACFM.
The ideal gas law also tells us that pressure and temperature are directly
proportional. A similar conversion is used to adjust to standard pressure.
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What is the operating temperature when oxidation is occurring at the site of the catalyst?
Global Technologies offers several types of catalysts to meet specific operating conditions. Each
catalyst type features unique properties that allows us to service a wide range of applications. All Global
catalysts have undergone extensive technical development and field testing. The factors which
determine the optimum catalyst are the amount and type of VOC, and the desired destruction
efficiency. In a typical gasoline remediation application, a minimum catalyst inlet temperature of 550° -
600°F is typical. The outlet temperature will depend on the VOC concentration. In a chlorinated solvent
application, a minimum catalyst temperature of 600°F AND a minimum catalyst outlet temperature of
900°F are typical.
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What is the lowest temperature at which Chloro-Cat units have continuously and successfully (at least 4
months) operated?
For most chlorinated solvent remediation applications, we recommend setting the Chloro-Cat to maintain
a catalyst outlet temperature of at least 890°F. Certain applications (for example, low halohydrocarbon
concentration and high hydrocarbon concentration) may allow for lower operating temperatures, but
as a general rule, applications with chlorinated solvents require a minimum outlet temperature of 890°F.
Global's experience in providing catalytic oxidizers for chlorinated sites is second to none. We have
supplied the Global Chloro-Cat to over 75 chlorinated sites around the world.
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Are there provisions for cooling the components as well in hotter (plus 100°F) weather?
In general, additional provisions for hot weather are not necessary. However, it is necessary to consider
the site location when specifying and building the oxidizer. For example, fan requirements are much
different in Denver due to the increased elevation.
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What about halogenated compounds?
Sometimes the contaminants that need to be remediated are halogenated (chlorinated, fluorinated and brominated) compounds. Until recent advances in catalyst
technology, thermal oxidation was the only way (and a very expensive way) to treat these compounds. Thermal oxidation requires higher temperatures
and complex metallurgy, resulting in higher capital costs and increased operating costs. Global Technologies partnered with catalyst technology
companies to develop catalysts capable of oxidizing halogens. The improved Global catalyst technology greatly reduces operating costs and provides a cost-effective solution for treating complicated halogen contaminants.
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What about sulfur-bearing compounds and the lead at gasoline sites? How do these contaminants effect oxidation technologies?
Sulfur and lead in an airstream have no effect on a thermal oxidation system.
Sulfur and lead are among contaminants (silicone, phosphorous and heavy
metals are others) that could potentially reduce the destruction efficiency
of a catalytic unit. Sulfur compounds that can be found on a remediation
site (usually a crude oil site) include H2S and other cyclic aromatics.
Luckily this is quite rare. If the presence of sulfur is identified before
equipment selection, specialty catalysts can be selected that are immune
to the masking/coating reaction that sulfur can have on standard remediation
catalyst. In addition, if sulfur contamination or masking is found in a
system after commissioning it can be "burned off" the catalyst bed by operating
at an elevated temperature for a short period of time.
Lead from gasoline is hardly ever a concern for catalytic technology. This
is due to the structure of the lead contained in leaded gasoline-tetraethyl
lead. Tetraethyl lead, however, quickly bioremediates to elemental lead
as soon as contacted by air in the SVE process. Elemental lead is too heavy
to be pulled from the wells in the SVE process. Global has never seen deactivation
of a catalytic remediation system as a direct result of the remediation
of a leaded gasoline station site.
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I've heard about Carbon Adsorption. How does oxidation compare?
Carbon Adsorption is most efficient when remediating sights with low airflow
(<100 SCFM) and low VOC concentration (<10 ppmv). You can call Global to
help you calculate Carbon Adsorption usage versus oxidation. As a guide
to carbon usage, use these formulas:
- 1 lb/BTEX requires 4.5 lbs/carbon
- 1 lb of carbon = $2.00 (includes supply and transportation)
- lbs/Hr = (ppmv) x (SCFM) x (60 min/Hr) x (Vapor Density), divided by 1,000,000
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People often use LEL, vapor concentration, and mass loading when dealing with an oxidation device. What do these terms mean and how are they related?
The LEL (Lower Explosive Limit) is the concentration of vapors (i.e. gasoline)
in an airstream that would cause an explosion in the presence of an ignition
source and the proper oxygen content. For gasoline hydrocarbons such as
benzene, toluene, ethyl benzene and xylene (BTEX) the LEL is approximately
12,000 ppmv. PPMV (parts per million by volume) signifies the concentration
of a constituent (by volume) in an airstream. In other words, 12,000 ppmv
BTEX means that for every 1,000,000 parts of an airstream, 12,000 are BTEX.
Concentration (ppmv) can be easily converted to a mass loading once two
factors are defined: airflow and vapor density. Airflow is simply the rate
at which air is moving; it is normally expressed in SCFM (standard cubic feet
per minute). Vapor density is the "weight per unit of volume" of the constituent
being "converted" from ppmv to lbs/hr. Vapor density is normally expressed
in lbs/ft3. BTEX, for example, has a vapor density of about 0.25 lbs/ft3.
Air, as a comparison, has a vapor density of 0.075 lbs/ft3. The conversion
formula from ppmv to lbs/hr is:
lbs/Hr = (ppmv) x (SCFM) x (60 min/Hr) x (Vapor Density), divided by 1,000,000
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What is the difference between regenerative blowers, positive displacement blowers and vacuum liquid ring pumps? Why should one be selected over another at a SVE site?
This question has a very straightforward answer. Vacuum levels normally dictate the blower required. A rule of thumb for blower selection:
- Regenerative Blowers: 0" H.G. to 8" H.G.
- Positive Displacement Blowers: 3" H.G. to 18" H.G.
- Liquid Ring Blowers: 18" H.G. to 27" H.G.
Regenerative blowers do not have clearances on their rotating parts as "tight"
as positive displacement blowers. As a result, their vacuum capabilities
are not as great. The advantages, however, are lower maintenance costs (lubrication)
and lower sound levels. Liquid ring pumps/blowers utilize water or another
"rotating part" sealing mechanism to achieve higher vacuum levels than PD
blowers.
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What are some other vapor treatment technologies?
There are other types of treatment for treating the compounds that are extracted
from the ground. Each has its own advantages and disadvantages. The advantage
of Carbon Adsorption is low initial cost. The disadvantages are high operating
costs for high solvent loadings, the need for breakthrough monitoring and
the requirement for offsite disposal of the spent carbon.
An Internal Combustion engine is also an alternative. It is portable, self-contained
and has a high destruction efficiency. The disadvantages associated with
internal combustion are high capital and operational costs, frequent maintenance,
limited range of applications and the high cost to operate at low solvent
loadings. It is often considered for low air volume (<250 SCFM) and high
concentration sites.
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What about treatment in densely populated or residential areas?
Densely populated and residential areas are often treated with SVE technology.
Global products offer sound-dampening cabinets with lockable, double-hinged
doors. Our integrated controls and first-out detection devices ensure safe
operation. With Global's unobtrusive, enclosed design, you can safely treat
a site without the appearance of bulky equipment.
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Is Global's system safe for bulk terminal sites?
Yes. Normally a general classification system is acceptable for a bulk terminal
site. Global also offers NFPA Class 1, Division 1 or Class 1, Division 2
rated explosion-proof motor, starter and electrical wiring. You can be certain
that your safety concerns are our priority.
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