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Hydrocarbon Splitting Processes

Steam Reforming of Natural Gas

Steam reforming of natural gas is a technically and commercially well established technology on industrial scale and currently the most economical route. Reforming technology is mainly used in the petrochemical and fertilizer industries for the production of so-called “on-purpose” hydrogen. Steam methane reforming (SMR) takes place at typically 850°C in the presence of an iron or nickel catalyst. The main processes of heat transfer are radiation and convection. The equilibrium composition of the reformer gas is depends strongly on the fuel characteristics, the steam-to-carbon ratio, outlet temperature and pressure, which are chosen according to the desired products. High reforming temperatures, low pressures and high steam to methane ratio favour a high methane conversion. Optimum pressure range is 2.5-3 MPa resulting in a hydrogen yield of 86-90% (Uhde:2003). A minimum H2O/CH4 ratio of around 2 is necessary to avoid carbon deposition on the catalyst. If excess steam is injected, typically 300% away from the stoichiometric mixture, the equilibrium is shifted towards more CO2 at temperatures of 300-400°C increasing the H2 yield and reducing the undesired production of carbon. The conventional process requires additional stages of desulfurization, CO shift conversion, and purification by pressure swing adsorption (PSA). Overall, the different process steps need considerable amount of energy. The total balance for such a plant is that 1 Nm3 of methane allows the production of 2.5 Nm3 of hydrogen, which corresponds to an overall efficiency of the process of around 65 %. It is rather difficult to get much higher efficiencies in practice.

Presently large steam reformer units with up to about 1000 splitting tubes have a production capacity of around 130,000 Nm3/h. Future reformer plants are designed to produce 237,000 Nm3/h or more. Modern steam-methane reformers often use more than one catalyst at different temperatures to optimize the H2 output. Advanced reforming techniques will operate by means of micro-porous ceramic membranes made of Pa-based alloy and a Ni-based catalyst, which can perform steam reforming reaction, shift reaction, and H2 separation simultaneously, i.e., without shift converter and PSA stages. The simultaneous processes allow to lower the reaction temperature down to around 550°C posing less stringent requirements to the materials. Such systems are compact and may provide higher efficiencies. Technical feasibility of the membrane reforming system was demonstrated by the Tokyo Gas Co., Japan, with test runs up to 1500 h achieving a hydrogen production rate of 15 Nm3/h and a 76 % conversion of the natural gas (HoriM:2004). Tests with a production rate of 40 Nm3/h were also conducted. Catalysts and the separation membranes are the key components, which still have potential for further improvement and optimization.

Smaller SMR units for local H2 production have a capacity around 150 Nm3/h. They are presently in the development and demonstration phase and are becoming increasingly powerful and efficient. Research in reforming technologies is concentrating on finding the right balance of fuel, air, and water flows for optimal processing.

Steam reforming units ranging from micro/milli scale to large scale can be constructed using the so-called “Printed Circuit Heat Exchangers”, PCHE. These are highly compact, robust, all-metal blocks composed of stacked metal plates, which contain alternately channels for the primary and the secondary fluid. The manufacturing technique, which is similar to printing electrical circuits allows complex flow channel geometries etched into the metal surface. Pressures of 50 MPa and temperatures of 900°C are possible (HEATRIC).

Onboard reforming in vehicles

For mobile applications Hydrogen may also be produced on board, e.g. in vehicles using e.g. methanol.

Partial Oxidation and Autothermal Reforming of Hydrocarbons

Partial oxidation of heavy oil and other hydrocarbons is a large-scale H2 production method, which is generally applied when generating synthesis gas from heavy oil fractions, coal, or coke. By adding oxygen, a part of the feedstock is burnt in an exothermal reaction. Its combination with endothermal steam reforming may lead to reactions without heat input from the outside (autothermal reforming - ATR) achieving higher efficiencies. Non-catalytic POX takes place at temperatures of 1200-1450°C and pressures of 3-7.5 MPa (Texaco process), the catalytic POX at around 1000°C. The resulting synthesis gas with a H2/CO ratio of ~2 (compared to > 3 for SMR) makes methanol synthesis an ideal follow-on process. Efficiencies of about 50% are somewhat less compared to SMR. Disadvantages are the need of large amounts of oxygen, catalyst deactivation due to carbon deposition, the byproduct CO, which requires the shift reaction, the need for gas purification stages. It may become competitive, where cheap primary energy is available. (reason : Cost of oxygen = capital cost + cost of electricity)

ATR technology was developed since the late 1970s with the goal to have the reforming step in a single adiabatic reactor. Preheated feedstock is gradually mixed and burnt in the combustion chamber at the top, where partial oxidation takes place. Steam is added to the feed to allow premixing of CH4 and O2. The steam reforming step is done in the lower part of the reactor. ATR requires 10-15% less energy and 25-30% less capital investment (BharadwajSS:1995). Catalytic autothermal reforming is ideal for fuel cell systems due to its simple design, low operation temperatures, flexible load, and high efficiency. It can be conducted in both monolith reactors and in fluidized bed reactors, but also in fixed bed micro-reactors. Plants usually include also air decomposition, unit size also in the order of 100,000 Nm3/h. Capacities of combined autothermal reformers are typically between 4000-35,000 Nm3/h, a range where “normal” steam reforming exhibits high specific investment. Small-sized units of POX reforming for mobile applications are presently under development.

Present methanol reformers are of fixed-bed type. Drawbacks are hot and cold spots and slow response due to slow heat transfer. Improvement has been achieved by using washcoated heat exchangers. A reasonable choice for portable FC applications is the employment of microreactors for methanol reforming. Micro-reactor means channel sizes with a cross section of 1000 micron x 230 micron plus a 33 nm thick Cu layer as the catalyst.

Coal Gasification

Gasification of coal is the oldest hydrogen production technology. Because of its abundant resources on earth, the conversion of coal to liquid or gaseous fuels has been worldwide commercially applied. At present, 20,000 MW of synthesis gas (H2 + CO) are being produced by coal, mainly for chemicals and power generation (Proc22ndWorldGasConference:2003). Various types of steam-coal gasification processes on a large scale exist such as Lurgi, Winkler, Koppers-Totzek, Texaco, which differ by the type of reactor, temperature and pressure range, grain size of the coal, and its residence time. Partial oxidation of pulverized coal by oxygen and steam in a fluidized bed takes place at about atmospheric pressure, where 30-40% of the coal are transformed to CO2 to supply splitting energy of water. The reaction rate strongly increases with temperature; typically temperatures up to 2000°C and pressures up to 3 MPa are selected. Main disadvantages of coal gasification are the handling of solid material streams and the large amounts of CO2, SO2, and ash requiring a complex cleaning system. In the hydro-gasification process, a high degree of gasification can be obtained already with relatively short residence times of 9-80 min. Of advantage compared with steam-coal gasification is the 200 K lower pre-heating temperature which reduces potential corrosive attack. A major drawback, however, is the large amount of residual coke of up to 40%. Its importance for H2 production is decreasing.

The Integrated Gasification Combined Cycle (IGCC) is presently considered the cleanest and most efficient coal-fueled technique. With its gas turbine step prior to the oxygen/steam process and its intermediate stage of synthesis gas, it allows the removal of most carbon components before combustion. The separated CO2 stream is of high purity and therefore suited for disposal. Thermal efficiency is expected to improve over conventional coal-fired steam turbine. Partial oxidation of coal is economic for coal countries. Under “normal” conditions, IGCC is not competitive with SMR. As of 2003, commercial IGCC plants in the power range of 250-350 MW are being operated in the USA, Netherlands, Spain, and Japan.

Another advanced method is the HYDROCARB coal cracking process. The coal is decomposed in a thermal cracker to carbon black as a clean fuel and hydrogen as a byproduct fuel. The commodity carbon black outweighs the poor efficiency of for this method.

Plasma-Arc Process

In the plasma-arc process, methane (or other gaseous and liquid hydrocarbons) splitting takes place at temperatures around 2500°C yielding solid carbon separated from the gas stream. The efficiency was reported to be good and is expected to further improve. Hydrogen purity is 98% prior to the cleaning step, if natural gas feed is used. SINTEF in Norway is using a 150 kW laboratory plasma torch with coaxial graphite electrodes, but without CO2 or NOX emissions. In cooperation with Kvaerner, a 3 MW industrial-scale plant was constructed in Canada working since 1992. In 1999, the Kvaerner group has finally started the commercial operation of its first carbon black plant in Canada, which runs on oil or natural gas and is designed for an initial annual capacity of 20,000 t of carbon black plus 50 million Nm3 of H2. The byproduct hydrogen is recirculated to the plasma burner and used as process gas. The energy demand for the plant is said to be 1.25 kWh/m3 H2 (PalmT:1999). But also solar furnaces are under development using sunlight to provide the dissociation temperatures. Research efforts are concentrating on optimized concepts for gas injection, heat transfer, protection against undesired carbon deposition. The search for optimal catalysts to reduce the maximum temperature has led to Ni or Fe based catalysts to decompose CH4 in the range of 500-700°C (Ni) or somewhat higher (Fe). Activated carbon is seen as an interesting alternative for the 900-1000°C range (MuradovNZ:2005).

Biomass Gasification

The gasification of biomass H2 production by converting organic wastes is attractive for decentralized applications. The complete process includes drying of the feedstock, pyrolysis, where the organic substance is decomposed, autothermal or allothermal (outside heat source) gasification, and finally combustion of the fuel gas. The autothermal gasification in a fluidized bed results in a synthesis gas with typically 30% of H2, 30% of CO, 30% of CO2, and 5-10% of CH4 plus some higher hydrocarbons. Facilities for wood treatment are on the verge of getting commercial. Demonstration pilot plants in the power range of 1 MW are being operated in various countries. Some apply an autothermal process and use air instead of oxygen. The product gas, at a certain quality, may be routed to a fuel cell power plant. Still biomass conversion appears to be less convenient for H2 production and is rather employed for heat and electricity or for biofuel production.

Microbial Hydrogen Production

Research is underway to produce Hydrogen from microbial processes in organic waste.


Palm T., Buch C. and Sauar E. (1999) Green heat and power. Technical report 3:1999, The Bellona Foundation.(BibTeX)
Bharadwaj S.S. and Schmidt L.D. (1995) Catalytic partial oxidation of natural gas to syngas. Fuel Processing Technology, 42:109-127.(BibTeX)

 (2003) Proceedings of the 22nd World Gas Conference, 1--5 June, 2003, Tokyo., Office of the Secretary General, StatoilHydro, Oslo, Norway, International Gas Union.(BibTeX) 

Hori M. et al. (2004) Synergistic hydrogen production by nuclear-heated steam reforming of fossil fuels. 1st COE-INES Int. Symp. on Innovative Nuclear Energy Systems for Sustainable Development of the World, Oct. 31-Nov. 4, 2004, Paper 43.(BibTeX)
Muradov N.Z. and Veziroglu T.N. (2005) From hydrocarbon to hydrogen-carbon to hydrogen economy. International Journal of Hydrogen Energy, 30:225-237.(BibTeX)
Uhde GmbH (2003) Hydrogen. {\tt}.(BibTeX)
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Page last modified on February 25, 2009, at 12:11 PM