Sasol’s latest investor report, released July 29, reveals that technical troubles at its pioneering Oryx gas-to-liquids (GTL) plant in Qatar are being overcome.
The plant has suffered from catalyst fines slip, caused by turbulence at the top of the Fischer-Tropsch reactor. Catalyst/wax separation is crucial to avoid contamination of final product, so further filtration equipment is being installed.
Here’s what Sasol says about Oryx in its latest report:
“The first scheduled shutdown of the Oryx GTL plant at Ras Laffan, Qatar was undertaken during the first quarter of 2008. The shutdown was completed successfully within the scheduled timeframe with no recordable injuries.
“Oryx GTL took advantage of the shutdown to conduct scheduled integrity maintenance and inspection work on the plant. Predefined modifications to the two Fisher-Tropsch reactors were also implemented during the first quarter of 2008.
“After implementing the modifications the reactors have been operating at high loads and all indications are that the modifications have been successful.
“The performance and production ramp-up of Oryx GTL is meeting our expectation. For most of June 2008, the plant operated above 85% of capacity with an average production for June of more than 22,000 barrels a day (b/d) of final product. The average production for the six months to June was about 30% higher than the previous six months.
“The superior-quality GTL products produced at the Oryx GTL plant are well accepted by the market, with GTL diesel demanding premiums over crude derived diesel products. The GTL diesel is sold as a high-value blend component in European and Middle Eastern markets. To date, the GTL naphtha has been sold primarily as cracker feedstock to Asian ethylene producers.
“The implementation of additional downstream filtration and related equipment is proceeding to plan and will be installed in the second half of 2008. As plant operating efficiencies increase, higher and more sustainable production levels are being achieved.”
Meantime, the proposed Nigeria “Escravos” GTL plant remains under “review,” Sasol says, “following its expected capital cost increasing to US$6 billion and completion date delayed to 2011.”
As for its proposed China coal-to-liquids (CTL) projects, Sasol said that it approved spending U.S. $140 million for its share of the “second phase of the feasibility studies to determine the techno-economic viability of developing an 80,000 b/d CTL plant each in the Shaanxi Province and the Ningxia Hui Autonomous region.
“The appointment of engineering contractors should follow and we expect to complete the feasibility study within about 18 months,” Sasol said.
As for its existing CTL production in South Africa, Sasol said that fiscal 2008 production volumes “are expected to be slightly higher than FY 2007. However, the increase was offset by the impact of flaring during the start-up of the new Project Turbo selective catalytic cracker (SCC) and lower reformer and gasifier availability.
“Sasol’s R14.5 billion [U.S.$1.96 billion] Turbo fuels-optimization and polymer-expansion project is largely completed with the two polymer plants running and the selective catalytic cracker (SCC) contributing to the viability of Sasol’s Secunda fuel pool, but not yet operating at full loads.
“The SCC has operated satisfactorily for five months – and with no reportable safety incidents – to produce and dispatch products to Sasol Polymers and the Secunda fuel pool for producing high-octane petrol.
“The SCC, the heart of Sasol Synfuels’ Turbo investment, was designed to convert almost one-million cubic meters a year of gasoline precursors into higher-octane gasoline, as well as the ethylene and propylene monomers required for the downstream production of polyethylene, polyvinyl chloride and polypropylene. The SCC commenced beneficial operation in January 2008 and has met most initial operational requirements.”
On the retail fuel sales front in South Africa, gasoline sales growth is weakening because of higher prices, Sasol said.
“Diesel sales, however, have been growing more vigorously because of the cumulative effect of ongoing growth in the transport and retail sectors and the increasing demand for backup electricity-generating capacity,” Sasol said.
Similarly, “sales of jet fuel continue to grow steadily in line with the increasing air traffic volumes between Johannesburg and major cities around the world.”
Complete fiscal 2008 results will be announced September 8, Sasol added.
-- Jack Peckham
Contrary to widely held beliefs that coal-to-liquids (CTL) diesel must be much worse on net CO2 than crude-based diesel, corn-ethanol or coal-to-electric power for vehicle fuel, CTL’s vast advantage over its competitors in net Btu/mile could turn that argument on its head, a new study shows.
Below is the complete text of a new study by Randall Harris, a former senior engineer for U.S. Dept. of Energy’s National Energy Technology Laboratory (NETL). Harris is now a technical consultant on energy projects in .
According to Harris’s calculations, CTL easily beats the competitors in net Btu/mile, even when a CTL plant is operated without CO2 capture & storage (CCS).
Before we get to Harris’s study itself (below), here’s his explanation to this question we posed:
Gasification News: When you show net CO2 on CTL, are you assuming (or not assuming) CO2 capture & storage (CCS) at the CTL refinery? Without CCS, a CTL plant is going to give off an awful lot of CO2 at the plant, because coal is so carbon-rich, compared to crude oil or corn for ethanol. This has to be accounted-for. How do you account for it?
Harris: “In looking at CO2 emissions from a crude oil refinery, not all the carbon associated with the crude can be assigned to one product. It is prorated based upon the carbon content of the various products. Those refinery products that go to (for example) plastics never emit their carbon in the form of CO2. So they are counted as carbon in the crude that ended up in the atmosphere.
“In most of the CTL plants the same is happening. The diesel or gasoline produced, and which will be combusted, will indeed eventually emit most of their carbon content as CO2 (at a rate based upon the combustion efficiency of the engine). That portion of the carbon in the coal that goes to (for example) naphtha that is destined for the plastics industry will likewise never be emitted as carbon dioxide.
“There are two standards being applied to this debate. This doesn’t serve the policy makers well.
“Some number of carbon atoms will be locked in finished products that won’t be combusted, while some will be. Only those that will be combusted should be of concern to the debate.
“Additionally the co-feeding of a biomass with coal, as many CTL projects are contemplating, further complicates the issue as biomass comes with negative carbon credit.
“For instance, if you co-feed wood waste as with coal, then the carbon from the approximately 1/6 of the tree that’s used in the gasifier carries with it the credit for the carbon in the 5/6 of the tree that is either still in the ground with the roots or is now furniture etc. (This is the USDA's carbon accounting system used in biomass projections.).
“The net effect is that wood credit effectively offsets some of the carbon from the coal reducing the effective carbon foot print of the project. If a CTL plant co-feeds enough biomass, then it can offset the carbon footprint enough that the CTL fuel is equal or lower in net carbon emissions to that an oil refinery for the same product.
“Let’s sat you if you were to start with 1 ton of coal that is 75% carbon, you now have 1,500 pounds of carbon. That is typically converted to liquids in a CTL plant at rate of 2/3 diesel and 1/3 naphtha.
“The naphtha goes to the chemical industry for use in plastics. This leaves 1,005 pounds of carbon.
“The carbon content of diesel is approximately 6 pounds per gallon although CTL diesel has slightly less carbon content than crude diesel (but let’s assume here it’ not worth the argument.
“In the typical CTL plant, you get about 56 gallons of diesel per ton of coal (2 bbl * 2/3) which means that 336 pounds of the carbon leaves the plant in the fuel. That means 669 pounds are converted into energy within the plant and eventually is converted into CO2.
“The fact most authors neglect to discuss is that to convert a barrel of crude to diesel or gasoline requires the use of a lot of electricity and natural gas. Those are not normally discussed because it is hard to get data from refineries.
“In this article (below) you will see that a good approximation can be made using the energy balances. In this case, Sunoco refineries were chosen as they are some of the best of the refineries when it comes to controlling emissions.
“The short answer to your question about net-CO2 from CTL is that to convert a ton of coal to diesel you only have the coal input; the plant creates everything it needs from the coal itself.
“To convert a barrel of crude, especially the heavy sours we are importing now, requires electricity usually from coal, and hydrogen usually for natural gas. These generate carbon dioxide that must be added to total. You cannot just compare the carbon in a barrel of crude to the carbon in a ton of coal.”
Gasification News welcomes science-based commentary from industry, academic and government research experts on this study. Please send the comments to: jpeckham@hartenergy.com and also to randall.j.harris@verizon.net .
Relative net energy efficiencies of transportation options
August 6, 2008
By Randall J Harris
Director of Development, Mingo Hybrid Energy LLC
randall.j.harris@verizon.net
(Editor’s Note: Harris formerly was Senior Engineer and Advisor to the Director for Program Development for the National Energy Technology Laboratory. Prior to that, he was a special Assistant to the Assistant Secretary of Energy. He has worked at National Laboratory, Los Alamos National Laboratory, and Dept. of Energy’s Rocky Flats plant in various engineering management roles. He has degrees in physics, nuclear engineering and business administration).
Multiple paths exist for powering our transportation future. This paper examines the relative net efficiency of the thermal conversion processes from raw material to ultimate locomotion of comparably sized passenger sedans as a function of net energy input per mile driven.
One option examined is from the conversion of the chemical energy to electricity to charge an all-electric vehicle and another is from the same source into synthetic diesel fuel. Yet another is the conversion of the chemical energy in corn into ethanol.
The vehicles chosen were passenger sedans of similar size, features and price. They included the 2009 Javlon XS500, an all electric powered sedan, the 2009 VW Jetta TDi, a diesel powered sedan, and the 2009 Chevrolet Impala LZE, an E85 powered sedan.
Results are:
The coal to diesel option resulted in 935 net Btu/mile;
The coal to electric option resulted in 1,063 net Btu/mile;
The corn to ethanol option resulted in 2,799 net Btu/mile;
The crude to diesel option resulted in 3,168 net Btu/mile.
While not analyzed in this paper it is believed that a liquid-fuel/electric hybrid would result in the lowering of the effective values for both the ethanol E85 and crude diesel options.
Energy efficiency of coal to electric transportation
In many previous evaluations electricity is mistakenly assigned the value of 3,412 British-thermal-units per kilowatt-hour (Btu per kWh). However, this ratio does not adequately represent the true energy that goes into a kilowatt of electricity at the point of service (household plug). Rather this relationship is one that relates the work capable of being done by the electricity expressed as Joules then converting them into Btu’s assuming one-hundred percent conversion efficiency. The correct relationship when converting the chemical energy of coal into electricity is referred to as the “heat rate.” This value relates the thermal energy of the fuel used at the power plant in Btu’s to the plant’s electrical output in kWh. In this case coal was used because it represents over 50% of electric production in the
Accepted average heat rates by fuel type and technology in Btu per kWh are:
Means of Electric Generation | Coal | Petroleum | Natural Gas | Nuclear |
Steam Turbine | 10,164 | 10,424 | 10,490 | 10,434 |
Gas Turbine | -- | 13,155 | 11,664 | -- |
Internal Combustion | -- | 10,179 | 9,947 | -- |
The average coal fired power plant has a thermal conversion efficiency of 33% and uses 10,164 Btu per kWh with the best-in-class plants using 9,854 Btu per kWh according to a 2001 report commissioned by EPA.
To understand the real Btu/kWh it is necessary to review each step of the process. Electric transmission line loses are reported to be 7.2% taking this further loss into account puts the energy input required at 10,964 Btu per kWh.
When electricity is used to charge batteries for an electric car an additional loss occurs in the charging process. Since electric cars are designed to operate at a battery charge level no less than 30% battery charge and not exceed an 80% charge level. Based upon manufacturer reports it takes 8-10 hours to reach the full charge state. National laboratory studies have shown that charging from the partially discharged state to the fully charged state results in the additional loss of 45% of the electricity from the wall to the battery. That brings our kilowatt hour in the battery to 19,935 Btu per kWh with an 8 hour charge requiring 159,482 Btu.
News reports indicate that all-electric sedans will range in price from $30,000 to $50,000, and most will only be able to go about 100 to 150 miles before needing a charge with one model, the Javlon, from Southern California’s Miles Automotive, claiming 150 miles before it needs a charge. This would put the Javlon at a net 1,063 Btu/mile.
Energy efficiency of coal to diesel transportation
Using indirect gasification and the Fischer-Tropsch synthesis process one ton of bituminous coal can be converted to 63 gallons of synthetic diesel.
Even if we discount the by-products of chemicals and electricity that would be produced, one ton of coal containing 22,000,000 Btu's (2000 lb x 11,000 Btu per lb) would yield 63 gallons of Ultra Low Sulfur Diesel containing 8,757,000 Btu's (63 gallons x 139,000 Btu per gallon. That is an efficiency of 40% for coal to diesel plants compared to 33% for coal electric plants.
However, from this ton of coal these facilities also produce 21 gallons of naphtha with 124,950 Btu per gal which can used to make jet fuel or plastics for 2,623,950 Btu’s and at least 300 kWh of electricity at the same time which above we saw was equal to 10,618 Btu per kWh for an additional 3,185,400 Btu’s.
When taking those into account the 63 gallons of diesel the effective net energy is 2,947,650 Btu's for 63 gallons or 46,788 Btu per gal,
The 2009 VW Jetta TDi sedan listing at $25,000 is slightly larger than the Javlon and reportedly gets 50 miles per gallon. This would result in the Jetta TDi with a net 935 Btu per mile using coal derived diesel.
Energy efficiency of crude to diesel
Understanding the energy efficiency of converting crude oil into its various products is difficult. Not only does the range of products vary from refinery to refinery, but the type of crude processed varies. Reporting inconsistencies between companies make using the aggregate data maintained by the U.S. Energy Information Agency (EIA) difficult to use in the analysis of complete energy associated with specific transportation fuel. Fortunately several companies produce sufficient information across their refineries to provide an insight. One of these is Sunoco.
Sunoco has taken energy conservation seriously and produces energy consumption and trends across their many refineries and chemical plants. These reports are the basis for this analysis.
According to the 2005 Sunoco Annual Report and its 2005 SEC 10k filing, Sunoco refineries consumed 141,996,030,000,000 Btu of energy that year to process 882,000 bbl/day or 321,930,000 bbl for the year. That would give them an overall energy use per processed barrel of crude of 441,077 Btu.
The report indicates that 32.745% of its refinery products were in the form of middle distillates representing 46,496,600,020,000 Btu/yr for middle distillates on a simple weighted average.
The Sunoco refineries reported producing 319,500 bbl/day middle distillates which works out to 116,617,500 bbl/yr. By using the prorated energy consumption above that yields 398,710 Btu/bbl middle distillates or 9,493 Btu/gal.
Sunoco used predominately light-sweet crude, however, because of tightening supplies began using some high-acid sweet crude in 2005 accounting for some 20,440,000 bbl of its inputs or about 6%.
Assuming that middle distillate fuels are mostly diesel that would mean an efficiency of 93.17% if you looked at it as energy consumed over energy produced.
While this is often the approach taken when discussing refinery efficiency it neglects several critical components of the refinery process. In this analysis we will start with the chemical energy in the crude and see how that changes through the refinery process.
We therefore start with the 5,800,000 Btu/bbl commonly used value for crude oil and say that 32.745% of it was converted to middle distillates which would mean 1,899,210 Btu/bbl or 45,219 Btu/gal was converted to the standard 139,000 Btu/gal diesel fuel. That must mean that the energy content of the diesel had to have been enhanced by 93,781 Btu. In a refinery this is done with the addition of hydrogen which has an energy content of 51,500 Btu/lb, therefore, 1.82 lbs of hydrogen was chemically added to the liquid as it passed through chemical reactors in the refinery. Since that value far exceeds the energy use reported on the Sunoco reports we must assume that the Sunoco reporting excluded it as an energy input and must consider, as most refineries do, hydrogen as a chemical input.
Whether bought from a pipeline or made on site, the extra hydrogen most likely came from natural gas and since a catalytic autothermal reformer (ATR) used to convert natural gas to hydrogen achieves an average 90% conversion efficiencies, to add 93,781 Btu of hydrogen with natural gas at 1,027 Btu/scf and a 90% efficiency one would need at least 101 scf of natural gas not including the energy input of the ATR which is about 16 kWth. However, we will assume that all this energy came from recovered refinery heat. The result is an additional 103,727 Btu/gal to the net energy balance.
In summary, we have 45,219 Btu/gal from the crude plus 103,727 Btu/gal from the natural gas plus 9,493 Btu/gal from the refinery energy share for a total of 158,439 Btu/gal input. That yields a diesel product with 139,000 Btu/gal. Dividing that by the 158,439 Btu/gal net input we find an 87.7% thermal efficiency.
Again using the 2009 VW Jetta TDi sedan and its reported 50 miles per gallon fuel efficiency, this would yield the Jetta TDi at a net 3,168 Btu per mile on crude derived diesel.
Energy efficiency of corn ethanol transportation
The analysis of energy efficiency of corn conversion to ethanol is more complex as corn has alternative uses, mainly cattle feed, and the byproducts of the conversion, Distillers Dried Grains with Solids (DDGS), are also cattle feed. Thus care must be exercised when assigning energy used in production of ethanol to the main and co-products of the process. In the literature, there are multiple attempts to estimate the energy efficiency of ethanol production and the results vary widely depending on the assumptions made.
On analysis by Lorenz and Morris (1995) showed that the process energy used to convert corn into ethanol was on average essentially equivalent to the energy content of the ethanol itself. Table 1 shows the average, best practice, and state of the art values for ethanol production as of 1995. The efficiency of the process will have undoubtedly been increased since then.
Energy Used to Make Ethanol From Corn and Cellulose (BTU’s per Gallon of Ethanol)
| Corn Ethanol (Industry Avg) | Corn Ethanol (Industry Best) | Corn Ethanol (State-of-the-Art) | Cellulosic Crop-Based Ethanol |
Fertilizer | 12,981 | 7,542 | 3,869 | 3,549 |
Pesticide | 1,060 | 643 | 406 | 437 |
Fuel | 2,651 | 1,565 | 1,321 | 8,120 |
Irrigation | 7,046 | 6,624 | 6,046 | -- |
Other (Feedstock) | 3,395 | 3,248 | 3,122 | 2,558 |
Total (feedstock) | 27,134 | 19,622 | 14,765 | 14,663 |
Process Steam | 36,732 | 28,201 | 26,185 | 49,075 |
Electricity | 14,444 | 7,300 | 5,148 | 8,925 |
Bulk Transport | 1,330 | 1,100 | 800 | 1,330 |
Other (process) | 1,450 | 1,282 | 1,050 | 2,100 |
Total (processing) | 53,956 | 37,883 | 33,183 | 61,430 |
TOTAL ENERGY INPUT | 81,090 | 57,504 | 47,948 | 76,093 |
Energy in Ethanol | 84,100 | 84,100 | 84,100 | 84,100 |
Co-product Credits | 27,579 | 36,261 | 36,261 | 115,400 |
TOTAL ENERGY OUTPUT | 111,679 | 120,361 | 120,361 | 199,500 |
Net Energy Gain | 30,589 | 62,857 | 72,413 | 123,407 |
Percent Gain | 38% | 109% | 151% | 162% |
The above analysis makes several assumptions that need to be addressed. First, corn is essentially 60% starch and 40% protein and fat. Therefore the feedstock energy needs to be partitioned between the starch and the other corn components. This can be done on a weight basis although other assignment methods may also be applicable. Second, although the protein and fat have energy content on a calorific basis, they are ultimately cattle feed and therefore are not converted into heat energy for a useful purpose other than for feed. In fact, energy is expended on drying the DDGS to prepare it for feed purposes in most instances.
A more appropriate energy analysis for the production of ethanol using the Lorenz/Morris data is shown in the table below. In this analysis, energy for feedstock production is split between the starch content of the corn and the protein/fat content. Per Maier, Reisling, and Briggs (1997), corn is between 55 and 65% starch. A value of 60% is used in this analysis. Energy for ethanol production from starch is assigned to ethanol itself as the DDGS is cattle feed and there is no net energy involved in the direct use of corn as cattle feed which is the low energy pathway to providing corn to cattle. This analysis follows guidelines for LCA analysis of co-product emissions assignment.
Analysis Element | Corn Ethanol (Industry Average) | Corn Ethanol (Industry Best) | Corn Ethanol (Theoretical Best) |
Fertilizer | 12,981 | 7,542 | 3,869 |
Pesticide | 1,060 | 643 | 406 |
Fuel | 2,651 | 1,565 | 1,321 |
Irrigation | 7,046 | 6,624 | 6,046 |
Other (Feedstock) | 3,395 | 3,248 | 3,122 |
Total (feedstock) | 27,133 | 19,622 | 14,764 |
Allocated to Starch@60% | 16,280 | 11,773 | 8,858 |
Process Steam | 36,732 | 28,201 | 26,185 |
Electricity | 14,444 | 7,300 | 5,148 |
Bulk Transport | 1,330 | 1,100 | 800 |
Other (process) | 1,450 | 1,282 | 1,050 |
Total (processing) | 53,956 | 37,883 | 33,183 |
TOTAL ENERGY INPUT | 70,236 | 49,656 | 42,041 |
Energy in Ethanol | 84,100 | 84,100 | 84,100 |
Co-product Credits | 0 | 0 | 0 |
TOTAL ENERGY OUTPUT | 84,100 | 84,100 | 84,100 |
Net Energy Gain | 13,864 | 34,444 | 42,059 |
Percent Gain | 20% | 69% | 100% |
In this analysis, the energy content of the feed stock is not considered. Corn has an energy content of 8000 to 8500 btu/lb of dry matter by bomb calorimetry. On a wet basis, with 15.5% moisture content which is typical of corn and the median value of 8250 btu/lb, moist corn contains 6970 btu/lb. As with any energy analysis, the energy of the raw material and the energy used to produce the raw material must be considered in the energy balance. The details of this analysis are as follows:
Using an average yield of 2.5 gallons ethanol per bushel of corn, 22.4 lbs of corn per gallon of ethanol produced or 27,725 Btu of corn energy per pound of ethanol and including 31,068 Btu of energy that are used to convert corn starch into ethanol and distill to 100% EtOH. Together that is 58,793 Btu/gal of corn derived ethanol.
Total inputs are energy content of corn plus energy of corn production, plus energy for conversion of corn to ethanol including distillation to fuel grade ethanol. Output is one pound of fuel grade ethanol. Dividing the output energy by the input energy gives the efficiency of the process which is about 22%.
Several companies produce E85 sedans of similar size and performance as those used in the above reference cases. General Motors (GM) has made a major effort to offer E85 vehicles in all classes with the 2009 Chevy Impala LZE being closest to the two previously chosen sedans achieving an EPA rated 21 mpg on the highway. Since these vehicles use 15% regular unleaded gasoline we have to adjust for its energy contribution. Regular unleaded gasoline contains 114,100 Btu/gal.
If we take weighted averages of the two fuels on volume basis you get 85% of 58,793Btu/gal plus 15% of 114,100 Btu/gal or 67,089 Btu/gal. Using the EPA 21 mpg value published for the 2009 Chevy Impala LZE E85 yields an energy efficiency of 2,799 Btu/mi.
Values for the corn ethanol analysis calculation are available from internet sites footnoted or are common units:
Quantity | Description |
56 | lbs shelled corn per bushel |
47.32 | Equivalent dry weight of corn |
2.5 | gallons per bushel ethanol yield |
22.4 | Lbs shelled corn per gal ethanol |
13.44 | Lbs starch per gal of ethanol at 60% starch content |
6970 | btu/lb corn 15.5% moisture basis |
27134 | BTU Energy Input to produce corn for 1 gal of ethanol |
4105 | BTU Energy Input to produce corn for 1 lb of ethanol |
156128 | BTU content of corn used to produce ethanol per gallon |
23620 | BTU Content of corn used to produce ethanol per lb of ethanol |
27725 | Raw Material and energy for production of one lb of ethanol |
84100 | HHV BTU content of Ethanol |
6.61 | lbs/gal ethanol |
12723 | BTU/lb ethanol HHV |
8459 | BTU/lb content of DDGs |
5.82 | lbs of DDGs produced per gallon of ethanol |
0.88 | Lbs of DDGSs produced per lb of ethanol |
49231.38 | BTU of DDGS per gallon of ethanol |
7448 | BTU of DDGs per pound of ethanol produced |
81,089 | Average BTU expended to produce one gallon ethanol +DDGS |
31,068 | Average BTU expended to produce one pound of Ethanol (corn + energy) |
58,793 | Input BTU for one lb of ethanol and DDGS production |
0.216406004 | Energy Efficiency |