New Methanol Technologies Offer Alternatives to Dirty Fuels by Michael Karl Strätling Chairman Lurgi Oel•Gas•Chemie GmbH, Germany
ower generation in many locations still relies on the burning of relatively expensive liquid hydrocarbons such as naphtha and diesel. The trend to replace these with clean natural gas has been limited by the cost of gas pipelines and liquefied petroleum gas (LPG) supply chains. But new methanol conversion technologies are offering an alternative that is cleaner and more cost-competitive. These technologies include oxygen-blown natural gas reforming, Lurgi MegaMethanol® synthesis, and methanol conversion to dimethyl-ether (DME), the first derivative of methanol. Using low-cost gas –
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at US$0.5/MMBtu – the Lurgi MegaMethanol® technology will reduce the methanol production cost to US$65/t and the DME production cost to US$93/t. Developments are underway to decrease these costs an additional 20 percent or more through even bigger single-train plants. Methanol and DME available at low cost are attractive feedstocks for power production. They are sulfur free and easy to transport and handle. Gas turbines as well as internal combustion engines are proven to run on both these fuels. GT efficiencies increase up to 10 percent with methanol as fuel.
Why Change? Why is an engineering company investing a big portion of its considerable R&D budget in such development? There are three main reasons: 1) plentiful gas supply sources, available for about 130 years; 2) environmental aspects and regulations; and 3) "monetising" the abundant natural gas reserves in remote areas as well as associated gas, which normally is flared without benefit. The driving forces behind such change are the economic and environmental benefits from the use of natural gas, and both forces will support continuous innovation regarding gas-based technologies. We believe the introduction of our Lurgi MegaMethanol® process for plants with a production of 5,000 tons of methanol per day and more will result in methanol available at a constant low price in the foreseeable future. At this price, methanol becomes attractive as an alternative clean fuel for power generation. Dimethyl-ether (DME), the first derivative of methanol, also has a high potential as an alternative to conventional diesel fuel and as a feedgas for gas turbines in power generation. Both products are virtually sulfur free and burn without soot or particulate formation. This "indirect" use of natural gas is economically viable where logistics and infrastructure do not support the high investment required for a gas pipeline grid or LNG supply chain. Smaller power plants utilizing expensive naphtha or diesel are prime candidates for conversion to clean, low-cost methanol or DME. Natural Gas: A Key Feedstock and Fuel for the 21st Century Total proven gas reserves worldwide amount to approximately 140 trillion cubic meters1, which translates into a gas reserve-to-production ratio (that is, a gas reserve lifetime) of 61 years. Furthermore, estimated additional gas reserves will cover a lifetime of 65 years more. Compared with the reserve lifetime of 41 years for petroleum E. Europe & FSU and 230 years for coal, there is no doubt 6.8% that natural gas will be a key fuel component West. Europe in the 21st century2. 3.1% However, currently, a considerable portion of this reserve is wasted yearly (see Figure 1). Considering all factors, it’s not hard to understand the incentives for both engineers and environmentalists to come up with novel ideas for the utilization of this gas.
Lurgi’s MegaMethanol® Technology: A Basis for Clean, Low-Cost Fuels The MegaMethanol® process is appropriate for plants with a capacity of more than 1 million metric tons per year. To achieve such a large capacity in a single-train plant, a special process design is required. For this reason, Lurgi focused on the most efficient integration of syngas generation and methanol synthesis, and came up with an economical and reliable technology for the new generation of future methanol plants3 (see Figure 2). Autothermal Reforming. Pure autothermal reforming can be applied for syngas production whenever light natural gases are used as feedstock to the process. The desulfurized (and optionally pre-reformed) feedstock is reformed to synthesis gas at about 40 bar using oxygen as the reforming agent. Even when using pure methane as feedstock to the autothermal reforming, it is necessary to ensure that the synthesis gas, as the stoichiometric number, defined as (H2 – CO2) / (CO + CO2) on a mole basis, is below 2.0. The most economic way to achieve the required gas composition is a special operation mode of the methanol synthesis with a very high CO conversion and a suppressed CO2 conversion. The optimum composition is achieved by recycling hydrogen that can be separated from the purge stream downstream of the methanol synthesis by a membrane unit or pressure swing adsorption (PSA) unit. Combined Converter Methanol Synthesis. In this innovative concept, the compressed syngas is first used as a cooling agent on the tube side of the gas-cooled reactor (Figure 2). In the downstream water-cooled methanol reactor, the preheated gas is converted under near-isothermal conditions while the heat of reaction is
Middle East 14.7%
Africa 39.3% C&S America 11.6% North America 16.7%
Far East & Oceania 7.7%
Source:Energy Information Administration (EIA):"International Natural Gas Information" 14 Feb 2001,http://www.eia.doe.gov
Figure 1: Flared Natural Gas (1998)
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Figure 2: Simplified Diagram of Lurgi's MegaMethanol® Technology
utilized for the production of saturated steam. The partly converted gas is then routed to the shell side of the gascooled reactor, where it is converted to methanol in the catalyst bed. Due to the combination of heat exchange (to preheat the syngas) and reaction, a declining and therefore thermodynamically favorable temperature profile across the catalyst bed is established in the gas-cooled reactor, thus leading to very high per-pass conversion. The product gas is then cooled, and crude methanol is condensed, separated and sent to the distillation unit. The gaseous stream is recycled to the reactor loop after separation of a purge gas stream. This, in turn, is routed to the purge gas separation unit where H2 is separated and returned to the syngas, and from there to the synthesis loop to adjust the proper stoichiometric number.
Figure 3: DME Production by Methanol Dehydration
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The most important advantages of the water- and gas-cooled reactor concept are as follows: • High syngas conversion efficiency. At the same overall conversion, the recycle ratio is about half of the ratio in a single-stage, water-cooled reactor. • High energy efficiency. In addition to the highpressure steam generated in the water-cooled reactor, a substantial part of the sensible heat can be recovered at the gas-cooled reactor outlet. • Low investment costs. Capital cost savings of about 40 percent for the synthesis loop can be realized due to the omission of a large feedstock preheater, savings for other equipment due to the lower recycle ratio and by the 50 percent reduction of catalyst volume in the water-cooled reactor. • Large single-train capacity. Two single-train plants with capacities of 5,000 t/d are under construction. MegaMethanol® plants up to a capacity of 7,500 t/d can be designed as single-train plants. Its process and component designs are backed by Lurgi’s expertise, which includes 38 methanol plants, more than 100 steam reformers and 32 autothermal reformers. Summarising, the unique advantages of the Mega-Methanol technology result in methanol prices of about $65/t and make this process ideally suited to be part of Lurgi’s downstream methanol route from C1 to propylene and other chemical products, like acetic acid, oxo-alcohols, acrylic acid, acrylates and many more.
Lurgi’s MegaDME: Source of Another Clean Fuel DME is industrially important as the starting material in the production of the methylating agent dimethyl sulphate and is used increasingly as an aerosol propellant. In the future, DME could be an alternative to conventional diesel fuel or a feedgas for power generation in gas turbines. Both applications are based on large-scale production facilities in order to achieve an economic fuel price. Traditionally, DME was obtained as a by-product of high-pressure methanol synthesis. Since low-pressure methanol synthesis was established, DME has been prepared from methanol by dehydration in the presence of suitable catalysts. The dehydration is carried out in a proven fixed-bed reactor. The product is cooled and distilled to yield pure DME. A modification of the methanol synthesis would allow for co-generation of DME within the methanol synthesis loop. This technical path has two disadvantages. While dehydrating methanol, the water vapor content increases, thus enhancing the water-gas shift reaction. By converting CO into CO2, the quality of the synthesis gas deteriorates. The kinetics of the reaction of CO2 and H2 is lower than the one of CO and H2. As a result, the synthesis catalyst volume and the recycle loop capacity have to be increased. In addition, due to its low boiling point, a cryogenic separation is required in order to separate DME from the synthesis recycle loop. Because of these disadvantages of the co-generation of methanol and DME, Lurgi favors the concept of generating DME from methanol by dehydration. If a DME unit is added to the MegaMethanol® Plant as shown in Figure 3, the distillation of methanol can be reduced from a three-tower system to one tower, which is the Light Ends Tower. The end product of this tower is stabilized methanol with a water content of approximately 20 percent. The stabilized methanol is fed to the DME reactor, where methanol reacts to DME and water and very small amounts of light ends, like CH4, CO2, CO and H2. The reaction product is forwarded to the DME product tower, where DME and light ends are separated from methanol and water. The light ends are flashed and separated from the liquid DME product. Remaining DME in the light ends is recovered by absorption with stabilized methanol. Then the light ends are sent to OSBL as fuel gas. The bottom product of the DME product tower is fed to the methanol tower, where methanol and water are separated. The methanol is recycled to the DME reactor to minimise methanol losses. The major portion of the water is sent back to the feedstock saturator in the
synthesis gas production. The surplus is sent to OSBL as product water, which can be used for irrigation after minor treatment. In this process, all types and qualities of DME can be produced. The different specifications for fuel gas, power generation or chemical-grade DME can be achieved just by varying size and design of the towers. Plant Type DME capacity
Mega Methanol & Dehydration 5,000 t/d
Total Fixed Cost (EPC)
28.5 MMBtu / t MeOH 40.2 MMBtu / t DME US$415 MM
Cost of production
US$93/t DME
Natural Gas Demand
Table 1: Economics of the Lurgi DME process
The economics of the Lurgi DME process are summarised in Table 1, assuming the following general setup. All investment cost figures are budgetary estimates of +/- 20 percent accuracy. Specific site conditions cannot be reflected within these numbers. • DME product quality is at least 99.2 percent DME. • Natural gas consumption figures include energy demand for air separation and power generation. • Total fixed cost includes air separation, power generation and off-sites. • Natural gas price: US$0.5/MMBtu. • Depreciation: 10 percent of ISBL + owner’s cost (i.e., 20 percent of "EPC"). • Return on Investment: 10 percent of total fixed cost. • Operating cost for operator staff, plant overhead, maintenance labor and material are included. The figures show the superb economics of MegaMethanol® in combination with a separate dehydration step. Feasibility of Methanol and DME as Gas Turbine Fuel At least one important GT manufacturer has tested methanol and DME as fuel and studied the field extensively, and has come to the following conclusions. Methanol as GT Fuel4. Methanol is an attractive future fuel for stationary gas turbine engines. Tests have shown that, with system and
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DME as GT Fuel5. BP Amoco initiated key programs to test various fuel mixtures containing DME in the manufacturer’s test combustors with equivalent electricity production of nearly 20 MW. Later, BP Amoco collaborated with EPDC (Electric Power Development Corporation, Japan) to conduct additional follow-up tests. These tests showed that DME is an excellent gas turbine fuel with emissions properties comparable to natural gas. Estimated performance of a nominal 700 MW combined cycle power plant based on the GE 9E machine indicates that the heat rate using refrigerated DME (at minus 25 degrees C) would be about 1.6 percent lower than that using natural gas and about 6.3 percent lower than that using liquid naphtha. Based on the results of the extensive combustion test programs, the manufacturer is prepared to pursue commercial offers of DME-fired E class and F class heavyduty gas turbines. Such offers can be made with standard commercial terms, including guarantees of output and heat rate.
Given the availability of technologies for the production of low-cost methanol and DME and their proven potential as clean fuels, it remains an economic exercise to locate the most promising sites for their application. combustor modifications, methanol is readily fired and is fully feasible as a gas turbine fuel. Relative to natural gas and distillate, methanol can achieve an improved heat rate, higher power output due to the higher mass flow, and lower NOx emissions due to the lower flame temperature. The efficiency increase of methanol versus distillate can be about 10 percent. Since methanol contains no sulfur, there are no SO2 emissions. The clean burning characteristics of methanol are expected to lead to clean turbine components and lower maintenance than with distillate fuel. The manufacturer is prepared to make commercial offers for new or modified gas turbines utilizing liquid methanol fuel. Additionally, vapor methanol fuel is feasible with a special design of the fuel system to ensure the absence of a liquid phase that could occur during all modes of operation. For either liquid or gas, the gas turbine fuel system must be modified to accommodate the higher mass and volumetric flow of methanol (relative to natural gas or distillate). The low flash point of methanol necessitates explosion proofing. It also dictates that startup be performed with a secondary fuel, such as distillate or natural gas. Combustion validation testing is required to confirm operability and emissions.
Figure 4: 5,000t/d Lurgi MegaMethanol® plant,Trinidad, 2002
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Feasibility of Methanol and DME as Internal Combustion Engine Fuel Methanol is well proven in IC engines. Over time, methanol has powered large fleets of passenger cars, buses and trucks. Stationary power generators are available commercially in dual fuel design for distillate and methanol feeds. DME is attracting worldwide attention due to its potential as an ultra-clean diesel fuel alternative6,7. Initial diesel engine tests indicate that DME would lead to ultra-low emissions that would surpass California’s ULEV (Ultra Low Emission Vehicles) regulations7. Recently, DME-fuelled buses have been demonstrated8. By extension, stationary power generators will also be possible. Economics of Methanol and DME as "New Fuels" Given the availability of technologies for the production of low-cost methanol and DME and their proven potential as clean fuels, it remains an economic exercise to locate the most promising sites for their application. The low production costs quoted above lead to "delivered" energy costs of about US$4.2/MMBtu for methanol and US$4.1/MMBtu for DME.
This compares favorably to costs of naphtha/diesel/fuel oil in "gas supply restricted" areas like parts of India, Spain, the Spanish Isles and the Caribbean. Prices in these regions are reported as US$4.5/MMBtu for LNG (where available) and as US$5.5-6/MMBtu for naphtha/diesel, with peaks at 7.7 in special cases. Transportation diesel goes for US$4.8-6.1/MMBtu worldwide. With these figures, methanol and DME are competitive with traditional fuels in the regions considered. The full advantage in a specific place has to be determined by careful study, taking into consideration the local conditions and the costs of refurbishing for the "new" fuels. These costs will vary greatly with the type and age of the existing equipment. For some new power plants, investment cost reductions are possible because of the reduced heat rates in GT-combined cycle applications. In addition to these cost advantages, methanol and DME carry environmental and strategic benefits. Both "new" fuels are virtually sulfur free and display excellent combustion characteristics. Strategically, these fuels will be uncoupled from the petroleum market. The gas field owner/developer and the investor of the methanol/DME plant will be interested in entering long-term supply contracts with the receiving power generator. The selection between methanol and DME will depend on economic as well as psychological considerations. While the energy density of DME is 21 percent higher than that of methanol, transportation in LPG-type vessels is more expensive than in methanol tankers. This is reflected in the very similar "delivered costs" given above. While gas turbines are more easily switched to DME than methanol, the DME storage and handling is more expensive. While methanol is shipped and handled more easily than DME, it encounters problems as a health hazard in some places. And some regions, such as in Japan and parts of India, already have an LPG infrastructure in place that could easily be modified to DME. Conclusions There are abundant natural gas reserves providing low-cost feedstock for methanol and DME production. Our challenge is the better use of natural resources, especially in the case of associated gases still being flared today. Lurgi’s MegaMethanol® technology, based on low-cost natural gas, brings down the delivered cost of methanol to about US$4.2/MMBtu and of DME to US$4.1/MMBtu. This opens up a completely new field for methanol and DME in power production – a field we named MtPower.
Dimethyl ether, a traditional derivative of methanol, could be a promising alternative fuel for power generation, diesel, LPG or the manufacture of olefins when produced in large capacities. The production of DME by dehydration of methanol is more economic than the cogeneration of methanol and DME. MegaMethanol® plants up to a capacity of 7,500 t/d can be designed as single-train plants. Its process and component designs are backed by Lurgi’s expertise, which includes 38 methanol plants, more than 100 steam reformers and 32 autothermal reformers. Developments are under way for 10,000 t/d plants, reducing production costs again by more than 20 percent. ■ Michael Karl Strätling, chairman of Lurgi Oel•Gas•Chemie GmbH, has also served as chairman of Davy McKee AG and Lurgi Zimmer AG. Mr. Strätling began his career in 1966 with Dr. C. Otto & Company GmbH in Bochum, Germany. Subsequently, he became chief executive of the company’s Otto Argentina subsidiary in Buenos Aires, and in 1977 became director of procurement for the parent company with major activities in Asia. Mr. Strätling earned an M.B.A. from University Münster in 1966.
References Energy Information Administration (EIA):"International Natural Gas Information," 14 Feb.2001,National Energy Information Center (http://www.eia.doe.gov/emeu/international/gas.html). 2 Ad.R.Punt:"Shell’s Perspective on the GTM options," EFI:Gas to Market Conference,San Francisco,October 11-13,2000. 3 S.Streb and H.Göhna:"MegaMethanol®:Paving the Way for New Down-stream Industries," World Methanol Conference,Copenhagen (Denmark),November 8-10,2000. 4 GE Position Paper,Schenectady,May 2001 (business communication). 5 Dr.A.Basu,BP,and J.M.Wainwright,GE Power Systems: "DME as a Power Generation Fuel:Performance in Gas Turbines," PETROTECH-2001 Conference,New Delhi,India, January 2001. 6 T.Fleisch,J.McCandless et al,SAE paper 950064,1995. 7 R.Verbeek,J.Van der Wiede,SAE paper 971607. 8 Volvo,Statoil et al,"Demonstration of DME-fuelled City Bus," SAE paper 2000-1-2005. 1
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