Article pubs.acs.org/IECR
Modular Gas-to-Liquid: Converting a Liability into Economic Value Johannes G. Koortzen, Sabjinder Bains,* Lary L. Kocher, Iain K. Baxter, and Ross A. Morgan CompactGTL, Windrush Court Suite I, Abingdon Business Park, Abingdon OX14 1SY, U.K. ABSTRACT: The disposal of associated gas can be a significant impediment to remote oilfield development. Although several associated gas management options exist, most either are too costly or cannot be moved to the oilfield. The production of syngas can be achieved by a variety of techniques, but again some of these require a dedicated air separation unit, which adds complexity and safety risks to the facility. Fischer−Tropsch synthesis has been shown to produce high-quality fuels from syngas since the late 1930s. CompactGTL has been able to develop a proprietary SMR technology for the production of syngas, which is then used in the Fischer−Tropsch process to produce a blendable syncrude. The proprietary reactor designs and catalysts resulted in a significant reduction in the footprint of a gas-to-liquid plant, such that these could be installed on a floating production, storage, and offloading vessel for access to associated gas at offshore fields. To date, CompactGTL’s fully integrated gas-to-liquid plant is the first one of its kind being operated at a demonstration scale. This technology allows monetization of associated gas and/or avoids taxation by flaring of methane. gas-to-liquid (GTL) technology.1 The FT process was operated in Germany with nine plants at a combined capacity of 19800 bbl/day.2 After the Second World War, these plants ceased to operate, but interest in the FT process remained. In the 1950s, several plants started again using the FT process, one in Brownsville, TX, with a capacity of 10800 bbl/day based on methane and one in Sasolburg, South Africa, based on coalderived gas.2 During the oil crisis in the late 1970s, Sasol constructed two more FT process plants in Secunda, South Africa, with a combined capacity of the three plants of 180000 bbl/day.2 In the 1990s, two other FT process plants were built based on methane, Mossgas in South Africa and Shell in Bintulu, Malaysia, with capacities of 30000 and 12500 bbl/day, respectively.2−4 Since the turn of this century, two more commercial FT plants have been commissioned in Qatar, the 34000 bbl/day Oryx GTL and the much larger 140000 bbl/day Shell Pearl project, clearly demonstrating that Sasol’s and Shell’s technologies are proven for large commercial-scale plants. What is of note is the scale of these GTL facilities ranging from around 10000 to 140000 bbl/day. These plants occupy a large footprint (Shell’s Pearl plant is around 350 soccer fields) and require significant financial investments, $18−20 billion for Shell’s Pearl plant, including all of the upstream costs.5 Commercial-scale technologies do not apply to associated gas because the technologies benefit from economies of scale based on high feed rates and sustained gas flow rates. In order to monetize associated gas, modularization of the reforming and FT processes is required to reduce the overall plant footprint and overcome logistical constraints.
1. INTRODUCTION The disposal of associated gas can be a significant impediment to oilfield development in remote and deep-water locations, where there is no ready market for the gas. Several technologies exist in dealing with associated gas, such as liquefied natural gas (LNG), reinjection of the gas, pipeline, compressed natural gas (CNG), gas to wire, and using the gas as feedstock for various chemical conversion technologies, such as Fischer−Tropsch (FT) synthesis, dimethyl ether, etc. LNG requires a high degree of compression and cooling to transform the natural gas into a liquid. It also requires expensive special tankers to transport the LNG to market. Receiving LNG requires specialized terminals that revaporize the gas and feeds it into the local natural gas pipeline network. LNG is a proven commercial technology but is generally applicable only for large fields (see Figure 1).
Figure 1. Distinct market for modular GTL.
In the near future, increasing dependence on natural gas reserves for fuel production is expected because of the increasing difficulty of finding crude oil resources, as well as a greater interest in environmentally friendly fuels. The efficient conversion of natural gas to liquid fuels via FT synthesis has been a focus of research work since its discovery in the late 1930s, as part of © 2013 American Chemical Society
Special Issue: Recent Advances in Natural Gas Conversion Received: Revised: Accepted: Published: 1720
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Figure 2. Diagrammatical representation of the assembly of a modular SMR/combustion unit, starting with the combustion channels (a), followed by a plate (b), followed by the SMR channels (c), and then a plate (d), and then the process is repeated from a to d until the final unit has been assembled (e and f). Red arrows indicate the flow for the combustion process, while blue arrows indicate the flow for the reforming process.
heat for the SMR reaction.6 SMR is a high-temperature (700− 1100 °C) catalytic process that yields syngas from methane (CH4) and steam (H2O).7 Utilization of water as the oxidant in the SMR reaction results in CompactGTL’s plants not requiring an expensive air separation unit to provide pure oxygen. The reaction, as shown in eq 1, is reversible in nature.
2. DISCUSSION 2.1. Reforming. In order to utilize associated gas, it first must be converted into syngas, which is a mixture of hydrogen and carbon monoxide. The syngas can then be fed to the FT process for conversion into synthetic crude (syncrude), which can be stored and later blended into refining streams for further upgrading. Several technologies exist for converting natural gas into syngas, such as autothermal reforming (ATR), steam methane reforming (SMR), and partial oxidation (POX), to name a few. Apart from SMR, the other technologies rely on the use of oxygen as part of the process for converting natural gas into syngas. For ATR and POX technologies, air separation units are required that potentially have a large footprint and could translate into a requirement for a larger supply of feedstock. The CompactGTL modular SMR units catalytically combust natural gas or a natural gas/tail gas mixture with air to generate
CH4 + H 2O ⇌ CO + 3H 2
(1)
CompactGTL’s modular SMR reactor is shown in Figure 2. These reactors feature proprietary designs derived from plate and fin heat exchanger manufacturing techniques.6 The small channel size and close proximity of the combustion and SMR channels provide excellent heat transfer and high efficiency for the size of the reactor. These SMR reactors are as little as 1/10th the size of conventional SMRs for a given output. The small 1721
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size allows these units to be deployed in applications where size and transportability are important. This is a true example of process intensification. Modular plant design, incorporating multiple reactors in parallel, provides a flexible, operable solution to accommodate gas feed variation and declines over the life of the oilfield. Reactor production begins with an external plate, then the first combustion channels, followed by another plate to separate the combustion process from the SMR process. Next the SMR channels are added, again separated with a plate from the next combustion channel. This process is repeated, until a single modular unit has been produced, as shown in Figure 2. Depending on the application, the number of these pairs can be changed to achieve different size units. From the diagram, one can also notice that the combustion and SMR catalyst sections overlap to allow direct transfer of heat from the combustion channels to the SMR channels. CompactGTL uses combustion and SMR-coated catalysts manufactured by Johnson Matthey. This exclusive partnership resulted in rapid testing and the combined expertise of the two companies to produce superior catalysts. In order for this process to work effectively, the heat generated by the combustion catalyst needs to be transferred to the endothermic SMR catalyst to generate the desired operating temperatures of 700− 1000 °C. The catalysts are on a corrugated structure, making insertion and removal of the catalyst easier because this can be automated.8 The coating technology was developed by Johnson Matthey based on their extensive knowledge of automotive catalytic converter production. The corrugated inserts can be seen in Figure 3.
Cobalt-based catalysts have shown to be the preferred choice because of higher C5+ production and low water−gas shift reaction. Various supports can be used such as silica, alumina, titania, and silicon carbide. CompactGTL’s proprietary cobaltbased catalysts have been developed over the past decade, and this has been successfully scaled up in conjunction with our partner Johnson- Matthey.8,10−17 The modular FT unit is shown in Figure 4. The catalysts are on a corrugated structure, making insertion and removal of the catalyst easier because this can be automated. The corrugated inserts can be seen in Figure 3. The FT synthesis process is used to generate longer-chain hydrocarbons. The exothermic reaction occurs at an elevated temperature (typically between 190 and 280 °C) and at an elevated pressure (typically between 1.5 and 2.5 MPa absolute values), where H2/CO ratios are between 1.0 and 2.5, and in the presence of a catalyst such as iron, cobalt, or ruthenium. The preferred catalyst consists of cobalt (10−40 wt %) on an inert refractory material such as silica or alumina, containing a promoter such as ruthenium, platinum, palladium, or rhenium, which is less than 10% the weight of the cobalt. Upon application of the FT process, CompactGTL has developed and operated two-stage reactors, permitting higher conversion overall (up to 75%) while maintaining a lower per pass conversion (30−50%), which has enabled better control over suspected deactivation mechanisms, such as water oxidation and carbon formation.12,18,19 In order to operate a two-stage reactor system, the noncondensable gases can typically be recycled to the reformer or can be used in the combustion process, generating the desired heat for the endothermic reforming process, increasing the overall conversion, and assisting with heat transfer. CompactGTL has a significant patent portfolio including patents on the operation of such a reactor design. The process has been successfully tested in Brazil and approved by Petrobras, confirming that this is a viable solution to increase the overall performance of the FT process.12,19−21 At the end of the useful catalyst lifetime, approximately 3−5 years without regeneration, the catalyst will be recycled to retrieve the metals. 2.3. Applications. On the basis of the volume of natural gas and the location, numerous possibilities exist for utilizing natural gas. 2.3.1. Onshore Plants. The CompactGTL modular gas solution enables oil companies to resolve the issue of associated gas handling. Commercial plant designs range from 2 to 50 MMscf/day, producing 200−5000 bbl/day of syncrude using proprietary CompactGTL SMR and FT reactor modules (see Figure 5 for a plant layout from a conceptual design study). The modular plant design can be deployed where access to sites has challenging logistical constraints. Modular plants are well suited to field production decline, offering high turn-down capability and redeployment of reactor modules and therefore having the flexibility to match the plant to the production profile of associated gas (see Figure 6). As the field’s production declines, surplus modules can be “switched off”, providing operating efficiency and a reduction in costs. This solution is ideally suited for (i) fields producing 2−50 million standard cubic feet (MMscf) of associated gas per day, (ii) fields with reserves of up to about 400 million bbl of oil equivalent, (iii) fields where flaring is being phased out or heavily taxed, (iv) new fields where reinjection is not viable because of the low volume of associated gas and high reservoir pressure, the distance to market, a lack of onshore solutions,
Figure 3. Corrugated inserts for SMR, combustion, and FT.
2.2. FT Synthesis. As mentioned earlier, the FT process was first commercialized in the late 1930s. The FT mechanism is stepwise chain growth, utilizing the H2 and CO as building blocks.9 This process is very versatile because syngas generation can be, in theory, from any carbon source, utilizing various syngas generation processes. CO + 2H 2 → −CH 2− + H 2O
(2) 1722
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Figure 4. Diagrammatical representation of the assembly of a modular FT unit, starting with the coolant channels (a), followed by a plate (b), followed by the FT channels (c), and then a plate (d), and then the process is repeated from a to d until the final unit has be assembled (e and f). The blue arrows indicate the flow of the coolant medium, while the red arrows indicate the flow of syngas.
and the location of the reservoirs, and (v) new fields where reinjection is the only current viable option but results in significant capital cost, increased complexity of reservoir management, potential damage to the reservoir, and limits on oil production rates. 2.3.2. Onshore Hybrid Plants. The CompactGTL hybrid plant enables companies to resolve the issue of larger onshore associated and stranded gas resources. A hybrid GTL plant employs conventional reforming technology from established suppliers and integrates this with our own FT modules (see Figure 7 for a conceptual design plant layout). Because of the nature of conventional reforming, this solution is suitable for larger sustained gas flow rates because conventional reforming takes advantage of economies of scale for syngas production. CompactGTL has completed a number of client-funded studies confirming that this solution opens up additional options for stranded gas because it offers a lower capital and operating cost. This solution is ideally suited for (i) onshore fields producing 30−150 million standard cubic feet (MMscf) of gas per day,
(ii) fields with sustained gas flow rates, (iii) onshore fields where the distance to market, a lack of alternative solutions, and the location of the reservoirs restricts development of the field, and (iv) onshore fields where production is not economically viable because the local gas market is saturated. 2.3.3. Offshore Plants. From the outset, CompactGTL technology was designed for onshore and offshore applications. The exclusive, strategic partnership between CompactGTL and SBM Offshore has enabled integration of the modular GTL plant into a floating production, storage, and offloading (FPSO) facility (see Figure 8 for a conceptual drawing). The CompactGTL modular plant is designed to be integrated with FPSO oil production facilities. The plant is modular and, accordingly, has the flexibility to match the production profile of associated gas. As the field’s production declines, the number of active reactor modules can be adjusted to match the associated gas production profile over time, providing operating efficiency and a reduction in costs. 1723
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Figure 5. Conceptual plant layout for a modular GTL plant.
Figure 7. Conceptual plant layout for a hybrid GTL plant.
Figure 6. Reducing the number of modules over time.
The close relationship between the two reactors (SMR and FT) in the CompactGTL process is a vital element in the efficient management of the overall system. The two reactions are tuned to work together to maximize efficiency and minimize waste streams depending upon the specific application and location of the plant. The water produced in the FT reaction can be treated to remove impurities and recycled back into the steam reforming process. CompactGTL’s proprietary reactor technology enables the design of a highly self-contained plant operating a stable process that does not require an oxygen supply. The reactor design retains only a small volume of fluids, which makes the system ideal for wave motion in an offshore environment.
Figure 8. Conceptual design of a GTL-enabled FPSO facility.
Key attributes of the CompactGTL modular gas solution: Safety • No oxygen supply • Flameless • Low surface temperatures 1724
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Operability and reliability • High CO2 feed gas handling • Rich associated gas handling • No catalyst handling on site • Exchangeability of reactor modules with plant onstream Seaworthiness • Low liquid inventory • Low center of gravity • Motion insensitivity 2.3.4. Petrobras Commercial Demonstration Plant. In October 2006, CompactGTL announced an agreement with Petrobras, the Brazilian government-backed oil company, to produce syncrude from natural gas using a modular GTL plant. The goal was to demonstrate integration of the proprietary SMR and FT reactors into a fully integrated and functional GTL plant (see Figure 9 for a conceptual drawing). Figure 10. Fully integrated GTL commercial demonstration plant.
performance of the SMR and FT reactors and catalysts.22 Several Petrobras operators were trained in running the modular GTL facility. Blending studies were carried out by Petrobras, demonstrating the effective blending of the syncrude, with normal crude oil for upgrading.
3. CONCLUSION CompactGTL has successfully shown that, although technically very challenging, a GTL plant can have both a reduced footprint and high efficiency. The modular GTL plant concept was designed, engineered, installed, and operated at a scale that eliminates scale-up risk and is the first small-scale GTL demonstration plant in operation and has the technology approved by Petrobras for commercial deployment.
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Figure 9. Conceptual drawing of a fully integrated demonstration GTL plant.
AUTHOR INFORMATION
Corresponding Author
The CompactGTL team was supported by Genesis Oil and Gas Consultants Ltd. during the process design stage of the contract. The SMR and FT reactors were manufactured by Sumitomo Precision Products Co., Ltd., in Osaka, Japan, and because of CompactGTL’s modular, small-scale approach, the complete set of GTL reactors was dispatched to Brazil by air freight. Zeton Inc. was awarded the EPC contract for the balance of the plant, and the GTL demonstration plant was constructed at Zeton’s facility in Burlington, Canada. The GTL demonstration plant was successfully commissioned at Petrobras’ testing site in Brazil in 2010 (see Figure 10 for the commercial demonstration GTL plant). In 2011, Petroleo Brasileiro S.A.’s CENPES Research and Development Centre successfully concluded an extensive test program of the CompactGTL modular GTL plant and approved the process for wider use within Petroleo Brasileiro S.A. (Petrobras). The Brazil demonstration plant is the world’s first fully integrated small-scale GTL facility, at 200000 scf/day capacity, incorporating gas pretreatment, prereforming, reforming, waste heat recovery, process steam generation, syngas compression, FT synthesis, FT cooling water system, and tail gas recycling. This plant was operated at commercial operating temperatures and pressure and performed according to both CompactGTL’s and Petrobras’ expectations. The process was also independently validated by Nexant. The plant has operated for over 2 years, demonstrating the extent of the effective
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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REFERENCES
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