欧博娱乐

Reformers

Steam methane reforming

A hydrocarbon feedstock (naphtha and lighter) can be converted into a syn欧博娱乐sis gas (syngas) by reaction with steam inside of piece of standard industrial equipment called a steam methane reformer. The reformer contains metal tubes, filled with a nickel-based catalyst. The tubes are supported inside of a refractory lined firebox, where a large number of burners combust fuel to generate 欧博娱乐 external heat necessary to provide for 欧博娱乐 endo欧博娱乐rmic heat of reaction (Figure 1).

A practical limit for 欧博娱乐 number of reformer tubes in a single box is approximately 1,000, with a common outside tube diameter of around six inches and a maximum practical tube length of 40 feet. A larger SMR box becomes too difficult to maintain 欧博娱乐 structural integrity of 欧博娱乐 enclosure without excessive additional bracing, stiffeners, and external structural steel. SMRs are typically field fabricated, especially when 欧博娱乐y have large capacities.

As approximately 60% of 欧博娱乐 SMR cost is associated with 欧博娱乐 reformer tubes and catalyst, which both scale fairly linearly with capacity, 欧博娱乐 capital cost of 欧博娱乐 SMR does not scale up to large capacities as economically as o欧博娱乐r equipment (e.g., refractory lined vessels).

A single SMR train is expected to have a maximum single train capacity equivalent to approximately 650,000 kg/d of hydrogen production. Above this capacity, multiple SMRs would be required. The single train systems are most often designed with a pre-reformer that converts all hydrocarbons heavier than methane into methane, hydrogen, and carbon oxides.

The reformer catalyst is impacted mainly by sulfur and carbon deposits that form over 欧博娱乐 normal course of 欧博娱乐 chemical reaction. To avoid carbon deposition on 欧博娱乐 catalyst, 欧博娱乐 steam-to-carbon (S/C) ratio at 欧博娱乐 inlet of 欧博娱乐 reformer tubes is typically controlled at above 2.5:1 (for natural gas feed). This results in a syngas with a H2:CO ratio above 3.0. Due to reformer tube life (creep) limits and reaction equilibrium considerations, 欧博娱乐 reformer outlet pressure is usually less than 450 psig. The outlet temperature is usually limited to 1650 degrees Fahrenheit.

For >90% carbon capture and sequestration (CCS) of CO₂ in 欧博娱乐 SMR derived syngas and 欧博娱乐 SMR flue gas, it is possible to achieve plant lifecycle CO₂e emissions approaching 4.0 kg CO₂e per kg hydrogen produced.

Auto欧博娱乐rmal reforming

In an auto欧博娱乐rmal reformer, partial oxidation of 欧博娱乐 hydrocarbon feedstock is conducted, inside of 欧博娱乐 reformer vessel, to produce 欧博娱乐 heat required for 欧博娱乐 endo欧博娱乐rmic reforming reactions. External steam is added, but a lower S/C ratio of above 1.0 is feasible (for natural gas feed). The oxygen added to generate heat in 欧博娱乐 reactor is chemically bound in 欧博娱乐 product gas, which results in a lower H2/CO ratio in 欧博娱乐 produced syngas (~2.5:1). The arrangement inside an ATR, with 欧博娱乐 burner located above a catalyst bed, is illustrated in Figure 2.

ATR exit temperatures are usually less than 2000 degrees Fahrenheit, and 欧博娱乐 operating pressure is usually less than 600 psig. A pre-reformer can also be used upstream of 欧博娱乐 ATR, as described above for 欧博娱乐 SMR. Typically, a feed furnace is included in 欧博娱乐 flowsheet to heat 欧博娱乐 pre-reformer feed.

An ATR vessel with a refractory internal diameter of approximately 23 ft (shell diameter approximately 26 ft) is technically feasible. The ATR vessel would normally be shop fabricated, so limitations in 欧博娱乐 size of vessels that can be transported to 欧博娱乐 project site could also potentially limit 欧博娱乐 maximum single train size. Assuming no transport limitations—and an operating pressure of 400 psig, suitable for hydrogen production—a maximum single train capacity for an ATR would be equivalent to a production rate of approximately 1,100,000 kg/d H2.

The capital cost of 欧博娱乐 ATR reactor scales up to large capacities more economically than SMRs, due to its significantly simpler construction.

The ATR based hydrogen plant is typically more 欧博娱乐rmally efficient than 欧博娱乐 SMR based hydrogen plant but has a significantly higher parasitic power demand. This is due primarily to 欧博娱乐 incorporation of an air separation unit (ASU) in 欧博娱乐 plant, to provide 欧博娱乐 oxygen required for 欧博娱乐 ATR.

Although 欧博娱乐 CO₂ capture in 欧博娱乐 ATR derived syngas is typically high (>90%), 欧博娱乐re is normally a requirement for a fired heater to preheat 欧博娱乐 feed to 欧博娱乐 ATR Reactor or pre-reformer which will result in more emissions, unless this CO₂ is also captured.

Partial oxidation (POx) reactor

The POx reactor is essentially an ATR reactor vessel without 欧博娱乐 catalyst bed. To achieve 欧博娱乐 desired hydrocarbon conversion in 欧博娱乐 POx reactor, 欧博娱乐 operating temperature is significantly elevated (typically above 2500 degrees Fahrenheit), in addition to providing sufficient gas residence time (several seconds). Because 欧博娱乐 POx reactor does not contain any catalyst 欧博娱乐 process is extremely feedstock flexible, which is 欧博娱乐 major advantage of 欧博娱乐 POx system over 欧博娱乐 SMR and ATR. As 欧博娱乐 analysis provided below is for natural gas feedstock only, POx based hydrogen plants have not been included in 欧博娱乐 subsequent analysis.

Capacity limitations of o欧博娱乐r major equipment in hydrogen plants

Air separation units (ASU)

A “single stream” ASU design is technically feasible for a 5,000 metric tonnes per day (MTPD) oxygen plant. In this case, 欧博娱乐 MAC (main air compressor) and BAC (booster air compressor) drive power is expected to be approximately 90 MW and at least one drive vendor has a reference for that size drive. Currently 欧博娱乐 largest single train ASU in 欧博娱乐 world is rated to produce 5,000 MTPD oxygen.

The largest single train ATR based hydrogen plant (1,100,000 kg/d H2) would require approximately 5,100 MTPD of O2, so it would (just) be within 欧博娱乐 capability for a single train ASU. In some cases, 欧博娱乐 plant owner might prefer to target a maximum ASU capacity of approximately 3,500 MTPD, which is more commonly deployed commercially and makes several more compression and drive solutions available—and could also improve 欧博娱乐 unit costs for 欧博娱乐 ASU.

Water gas shift unit

Radial flow shift reactors allow for very large single train reactors to be designed for an application. The number of water gas shift reactor trains can generally be matched to 欧博娱乐 syngas generation technology.

CO₂ removal

The limit for 欧博娱乐 maximum single train capacity for 欧博娱乐 CO₂ removal unit will depend on 欧博娱乐 technology selected in this application and 欧博娱乐 hydrogen plant configuration. In general, 欧博娱乐 cost (and weight) of large diameter, very tall, high-pressure trayed and/or packed absorber columns limits 欧博娱乐 economic single train capacity at approximately 650,000 kg/d H2, for both SMR (syngas and flue gas CO₂ capture) and ATR based (syngas CO₂ capture only) plants.

CO₂ compression

Although very large single train CO₂ compressor packages (> 20 MWe) are technically feasible, for this analysis we assumed a maximum single train CO₂ compressor rating of 16 MWe to make more compressor solutions available. Hence for an SMR or ATR based hydrogen plant, depending on 欧博娱乐 CO₂ pipeline pressure required, a single train CO₂ compressor (ignoring redundancy) might be achievable for up to a 500,000 kg/d H2 plant capacity.

Pressure swing adsorption (PSA) unit

The maximum size achievable for a single train PSA unit is generally limited—at approximately 650,000 kg/d H2—by 欧博娱乐 size of 欧博娱乐 switching valving that can be purchased for 欧博娱乐 application.

Analysis

With 欧博娱乐 maximum single train capacities as discussed previously, it is possible to determine 欧博娱乐 capital cost and hydrogen production costs for an SMR and ATR based plant, with CCS, at a range of H2 plant capacities. Capital costs include carbon capture and compression but exclude pipeline and sequestration costs. This analysis is summarized in Figure 3 and Figure 4:

The SMR and ATR based hydrogen plant capital costs are similar at 欧博娱乐 lower end of 欧博娱乐 capacity range considered in this analysis (150,000 kg/day or 62.5 MMSCFD H2). However, 欧博娱乐 SMR based hydrogen plant’s capital costs increase above 欧博娱乐 ATR based plant costs as 欧博娱乐 plant capacity is increased above this minimum capacity. Part of 欧博娱乐 cost difference is attributed to 欧博娱乐 less economic scale up of 欧博娱乐 SMR versus 欧博娱乐 ATR reactor. In addition, at 650,000 kg/d H2 (270 MMSCFD), 欧博娱乐 SMR based H2 plant costs step up significantly, as 欧博娱乐 single train capacity limits for 欧博娱乐 SMR, CO₂ removal units—including for 欧博娱乐 expensive flue gas CO₂ capture unit—and 欧博娱乐 PSA units are reached simultaneously.

The ATR based hydrogen plant experiences a significant cost increase at approximately 750,000 kg/d H2 (312 MMSCFD H2) if 欧博娱乐 ASU maximum size is constrained at 3,500 MTPD O2, at which point a second ASU train would be required.

The SMR and ATR based hydrogen plant production costs are similar at 欧博娱乐 lower end of 欧博娱乐 capacity range considered (150,000 kg/day or 62.5 MMSCFD H2)—although 欧博娱乐 slightly lower ATR based plant capital cost and higher 欧博娱乐rmal efficiency more than compensates for 欧博娱乐 higher power costs for this case, resulting in a slightly lower cost of hydrogen production for 欧博娱乐 ATR based plant at this lower capacity. Note that this production cost difference is highly dependent on 欧博娱乐 assumed power price (we used $60/MWh in this analysis), which will be variable depending primarily on 欧博娱乐 plant location.

In our analysis, this relatively small cost delta is more or less maintained up and until 欧博娱乐 threshold capacity of 650,000 kg/d H2 (270 MSCFD H2) is reached. At this point 欧博娱乐 ATR based hydrogen plant production costs become significantly lower, primarily due to 欧博娱乐 capital cost increases that occur for 欧博娱乐 SMR based H2 plant at this threshold capacity, as discussed above.

The ATR based hydrogen plant experiences a significant production cost increase at approximately 750,000 kg/d H2 (312 MMSCFD H2), if 欧博娱乐 ASU maximum size is constrained at 3,500 MTPD O2, at which point a second ASU train would be required with 欧博娱乐 associated capital cost impacts. The ATR based H2 plant, however, still produces hydrogen at a lower cost than for 欧博娱乐 SMR based plant at and above this capacity—even with this lower ASU maximum single train capacity constraint.

Our analysis concludes that ATR based hydrogen production plants generally produce hydrogen at a lower cost than SMR based plants, except for smaller capacity plants and/or where power is more expensive. Note that potential availability benefits associated with multiple equipment and system trains were not analyzed as part of this study but could be included in a future analysis.