(some of the content below is from my 2022 book
Natural Gas and Decarbonization)
Propane
Propane is
well-known as the main component of liquid petroleum gas, or LP gas. LP gas is
mostly propane with some butane. It is one of the natural gas liquids (NGLs),
also known as hydrocarbon gas liquids (HGLs). The formula for LP gas can vary according
to source. In the U.S. the formula is 60% propane (C3H8) and 40% butane/isobutane
(both C4H10). About 70% of propane in the U.S. is made from natural gas and
about 30% is made from petroleum as of 2021. The chemical formula for propane
is C3H8. The lightest and least carbon emitting hydrocarbon molecule is methane
(CH4). Methane is the main component of natural gas. The second lightest
hydrocarbon is ethane (C2H6). Propane is the third lightest hydrocarbon. Ethane
is the hydrocarbon most present in natural gas after methane. Propane is third.
It has some advantages over methane (as compressed natural gas). It can occupy
a smaller onboard space for transport vehicles which gives it a longer range.
It can be easily transported in tanks via truck, rail, or even a car with small
home use tanks. Thus, it can easily be used in remote places where there are no
natural gas distribution lines. The emissions intensity of propane is higher
than that of methane but lower than gasoline. It is also the cheapest way to
make polypropylene which is a feedstock for plastics. It is still cheaper to
heat with natural gas than LP gas, but LP gas does provide a higher BTU heat.
Propane has great potential as a reasonably affordable and cleaner energy
source to replace wood, charcoal, and dung cooking fires in developing
countries, especially in Asia and Africa. These fires are very strongly
implicated in indoor air pollution which is well documented as a significant
health problem, especially among women and children in these countries.
Governments in those countries should promote, support, and perhaps subsidize
propane as a cleaner cooking fuel. Propane is also used as a transport fuel and
has many other uses from flame weeding to drying grain and fruit to cutting and
welding torches. Heaters, furnaces, stoves, smokers, BBQs, dryers, hot water
tanks, refrigerators, soldering tools, kilns, forges, livestock floor sanitizers,
industrial burners, jewelry melting and moulding tools, and other devices are
powered by propane.
Propane as
R290 is very likely to become a refrigerant of choice for air conditioners
around the world as it has very clear cost, performance and climate benefits
relative to the HFCs now being used. The chemical industry has pushed back as
they stand to lose market share and value from the change. They have argued
that propane as a flammable hydrocarbon is unsafe but experts have said that
those arguments are poor and rely on highly unlikely and extraordinary
situations that would make the R290 dangerous. I wrote about it in my 2022 book
Natural Gas and Decarbonization.
Propane can be
a useful alternative vehicle fuel offering only slightly less combustion carbon
emissions as gasoline and diesel, lower pollutant emissions, lower fuel costs,
lower operating and maintenance costs, and range. Fuel cost depends on the
“spread” between propane and gasoline/diesel, but propane is always cheaper.
Propane Autogas is becoming especially popular for Class 3-7 fleet vehicles,
notes a recent article in LPGas Magazine. This includes a lot of delivery, food
and beverage, and buses. Many US Postal Service contractors are using Propane
Autogas, saving about 40% over diesel costs. According to the DOE life-cycle
greenhouse gas emissions are reduced by 13% using propane since it is more
efficient to process it out from the natural gas stream than to make it through
oil refining. It has good carbon emissions reductions in the medium-duty truck
range, where it is being marketed the most. Compared to compressed natural gas
(CNG) propane offers smaller on-board fuel storage space. The Gas Technology Institute notes in their GHG
and Criteria Pollutant Emissions Analysis from 2017 that “Propane has
several advantages for fleets, including lower total-cost-of-ownership,
comparable performance to conventional fuels, onsite fueling, reduced maintenance,
and lower emissions. Small to mid-size fleets with high mileage and based at a
single location are one of the most cost-effective applications that can
benefit from lower fuel costs and reduced maintenance.” The same paper also
notes that propane has a similar fuel efficiency to diesel in the medium-duty
range which includes bobtail trucks. “For bobtail trucks, propane GHG emissions
are 11% lower and NOx emissions are 4% lower than comparable diesel vehicles.
SOx and particulates are also lower.
In Muskingum County, Ohio Sheriff’s
Department there are 20 of 31 primary response vehicles that are powered by
propane. These are added tanks and systems, at around $70K per vehicle.
Apparently, fuel savings, system life, and less maintenance are favorable to
economics. They began converting vehicles to propane in 2015. There have been
no safety issues and system performance has been good.
The Ohio
Propane Gas Association website has some data on comparative costs, carbon and
pollution emissions, and comparative maintenance costs. For medium duty trucks
the advantages are a 12% reduction in greenhouse gases and a 4% reduction in
NOx vs. diesel, decent but not stellar. For light duty truck the advantages are
36% reduction in NOx vs. diesel though only 5% less vs. gasoline. For light
duty truck greenhouses gases there is a 12% reduction vs, gasoline. For school
buses there is a 96% reduction in NOx for propane vs. diesel. This is important
since NOx from buses contribute to city smog. The chart below, adapted from the
data, shows more comparisons favorable to propane. It should be noted, however,
that electric has the lowest fuel, maintenance, and total operating costs per
mile by a wide margin.
|
|
total cost/mile |
maintenance
cost/mile |
fuel cost/mile |
bus purchase price
|
bus cost/lb. of
NOx reduced |
|
Propane |
$0.24 |
$0.06 |
$0.16 |
$95,000 |
$91 |
|
Diesel |
$0.53 |
$0.24 |
$0.28 |
$90,000 |
$1330 |
|
Electric |
|
|
|
$300,000 |
$268 |
Vehicle Fleet and
Bus Comparisons. Adapted from data from the Ohio Propane Gas Association.
Butanes (Normal Butane and Isobutane)
Butanes, the
other components of LP Gas also have many uses alone or in combo with propane. There
are two butanes, normal butane and isobutane, both C4H10. They have a vapor
pressure 3 to 4 times lower than propane which makes butane an ideal source as
a lighter fuel. A small tame flame is the result. In so-called “refined”
iso-butane, or iso-butane with impurities removed, concentrated flames in
special-made torches can heat up to 2700 deg F, which makes these specialized
torches applicable for many specific scientific, medical, construction,
soldering, and craft uses. Both butanes are also a common component in LP gas
(liquefied petroleum gas) but propane is typically the main component. Butane
is the lighter fuel of choice as well as being commonly used for camp stoves.
It is also used as an aerosol propellant and increasingly as a refrigerant that
replaces the CFCs (chlorofluorocarbons) and HFCs (hydrofluorocarbons)
implicated in global warming and making a hole in the ozone layer. Butane does
have one limitation as a heating fuel: it can fail to gasify in real cold
weather. This is why butane is not higher in LP gas. Since camp fuel is mostly
used in the summer, the butane canisters are popular. Butane is also a
feedstock for butadiene, a key component of synthetic rubber. Isobutane is the
preferred form for refrigerants and much of that is now coming from natural gas
processing of shale gas. It is mostly made from normal butane in isomerization
units at alkylate plants. Alkylate is made from isobutane and NGL byproducts.
Alkylate and normal butane are both used as gasoline additives. Butane lowers
vapor pressure and alkylate increases octane rating. Alkylate typically makes
up 11-13% of gasoline and more than that in the summer months. So, one can say
that NGLs (both butanes) are a significant feedstock for gasoline. Appalachian
wet shale gas has also increased normal and iso butane supplies.
In a similar fashion
to propane as the R290 refrigerant there is an isobutane refrigerant R600a that
has great potential for use in domestic refrigerators. R600a has better
performance, lower energy use, negligible global warming potential, and zero
ozone depletion potential compared to the HFC 134a. In 2019 R600a began to be
used in some U.S. refrigerators. The energy and cost savings are significant
and should be regarded as a significant decarbonization action as well since the
global warming potential of R600a is about 500 times less than that of 134a.
Natural Gas Liquids Exports from the U.S., Mainly
from Shale Gas
Natural gas liquid
(NGL) exports from the U.S. have skyrocketed since shale gas resources were unleashed
through horizontal drilling and high-volume hydraulic fracturing from around
2010. Through 2020 propane exports make up 60% of those exports. The main
reason is as its use as a polypropylene feedstock. Making propane or
polypropylene from petroleum is both more expensive and more carbon intense
than making it from propane. That is expected to continue as the highest number
of global petrochemical projects expected to be built and expanded between 2023
and 2027 are polypropylene projects. China is expected to have the most. As
noted, US exports of hydrocarbon gas liquids have increased dramatically since
2010. In those 11 years exports increased by a whopping 25 times from about 5
million barrels per day to about 75 million barrels per day. In 2020 Japan was
the biggest buyer followed distantly by Canada. China, Mexico, South Korea,
India, Indonesia, Brazil, the Netherlands, and the UK are also key buyers. For
2020 propane is by far the most exported natural gas liquid at 60% of all
exported NGLs followed by normal butane then ethane then natural gasoline then
isobutane. The graph below just shows the growth in HGL/NGL exports alongside
the growth in propane exports, the major component of HGL exports. Clearly, the
advent of shale gas production is the driver for this export growth. Ethane
exports from the US have grown by 20 times since 2014 after pipelines, export
terminals, and new ethane tankers were built. Normal butane exports have grown
similarly to ethane exports. In contrast, natural gasoline exports have grown
only very slightly in recent years and isobutane exports have dropped. Since
about 30% of propane is derived from oil refining that suggests about 18% of
total NGL exports could be derived from refineries rather than natural gas
wells if the average is similar with exports.
US Exports of Hydrocarbon Gas Liquids vs. US Exports of Propane. Data Source: Energy Information Administration
New Propane Recovery Innovation Announced That Will
Boost Natural Gas Processing Profitability
A new innovation
for propane recovery improvement at natural gas processing plants was recently
announced by BCCK, an engineering, procurement, fabrication, and field
construction services firm. The company reported in February that propane
recoveries were improved to greater than 99% in ethane rejection and that their
new design can also improve ethane recovery. Their new design utilizes a
skidded BCCK patent-pending design, the G2R-Flex, “which will be available
to enhance propane recoveries at many of the existing 200 MMSCFD gas subcooled
process (GSP) facilities operating throughout the United States.” This improvement
may be able to help many underperforming cryogenic natural gas processing plants
and boost their profitability at current propane prices. BCCK describes their
new design as a simple, efficient, and effective modification. They offer
complete turnkey capabilities through full EPC services on this new propane
recovery design. The new successful tests of the design were implemented at a
premier midstream group in Ohio’s Marcellus-Utica Basin.
New Innovation in Dividing Wall Column Distillation
Another innovation
announced in 2022 is a patent for dividing wall column distillation that can be
used to combine two distillation towers into one for the extraction of purity
products, or different NGLs or combinations of NGLs. Dividing Wall Column
distillation has been explored since the 1940’s. The design can potentially
lower both capex and opex by 20 to 50%. It is used for separating a
multicomponent mixture into three or more high purity product streams in a
single column. The method is being used more and more in refineries as company
DWC Innovations recounts on their website. DWC technology is able to combine
two distillation columns into one. Energy consumption, emissions, and costs are
reduced. Engineering firm, Burns & McDonnel
is adapting the method for NGL fractionation. They announced a patent on their
design in early 2022. This tech allows the usual four column NGL fractionation
facility to be reduced to three columns (fractionation towers) and still yield
the five purity products: ethane, propane, normal butane, iso-butane, and
natural gasoline. As noted, the tech can also be used in oil refineries and
chemical facilities. The new tech reduces footprint, carbon emissions, and
costs. Gas Processing News writes: “In 2019, Burns & McDonnell completed
construction of the first dividing wall column train in the NGL fractionation
industry for a confidential midstream company. The facility processes 125,000
bpd of Y-grade feed. The DWC methodology was successful in lowering capital
costs and providing significant operational and utility savings after startup.”
The tech can be customized and scaled for different facility requirements. With
lower capex, opex, and emissions this tech could become widely adopted in the
future.
References:
Natural Gas and
Decarbonization: Key Component and Enabler of the Lower Carbon, Reasonable Cost
Energy Systems of the Future: Strategies for the 2020’s and Beyond. Kent C. Stewart.
2022. Amazon Publishing.
Petrochemicals New
Build and Expansion Projects Analysis by Type, Development Stage, Key
Countries, Region and Forecasts, 2023-2027. GlobalData. February 1, 2023. Petrochemicals
New Build and Expansion Projects Analysis by Type, Development Stage, Key
Countries, Region and Forecasts, 2023-2027 (globaldata.com)
BCCK boosts propane
recovery at cryogenic gas processing facility. Gas Processing News. February
27, 2023. News (gasprocessingnews.com)
BCCK BOOSTS PROPANE
RECOVERY WITH NEXT-GENERATION TECHNOLOGY AT CRYOGENIC GAS PROCESSING FACILITY. BCCK
Boosts Propane Recovery with Next-Generation Technology at Cryogenic Gas
Processing Facility - BCCK
BCCK HOLDING COMPANY
TO ENHANCE RECOVERIES AT CRYOGENIC GAS FACILITY IN MARCELLUS-UTICA BASIN. BCCK
Holding Company to Enhance Recoveries at Cryogenic Gas Facility in
Marcellus-Utica Basin - BCCK
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