Steam reforming of natural gas

Natural gas is an odorless and colorless naturally occurring mixture of hydrocarbon and nonhydrocarbon gases found in porous geologic formations beneath the earth s surface, often in association with petroleum or coal. The principal constituent is methane (CH4) and its composition is regionally dependent. Table 2.2 summarizes the composition of natural gas by region.8 

Methane reacts with steam in the presence of a supported nickel catalyst to produce a mixture of CO and H2, also known as synthesis gas or syngas as represented by Equation 2.1. This reaction is also referred to as steam methane reforming (SMR) and is a widely practiced technology for industrial production of H2. However, the SMR is not really just one reaction as indicated in Equation 2.1 but involves contributions from several different catalyzed reactions such as water-gas shift 

Alternative technologies to the PSA process for H2 purification include, after the HTS reaction, a low-temperature shift (LTS) reaction followed by C02 scrubbing (e.g., monoethanolamine or hot potash).11 The LTS reaction can increase the H2 yield slightly. However, the product stream, after the HTS, needs to be cooled to about 220 °C. Preferential oxidation (Prox) and/or methanation reaction as shown in Equations 2.6 and 2.7, respectively, removes the traces of CO and C02. The product H2 has a purity of over 97%. 

As shown in Equation 2.1, the SMR reaction results in gas volume expansion and is strongly endothermic (A//298 = +205.9 kJ/mol). Therefore, the reaction is thermodynamically favorable under low pressure and high temperatures. The changes in 

Equilibrium H2 and CO compositions can also be derived thermodynamically. Depending on the ultimate application for the gas product, H2/CO ratio can be further tailored by integrating with secondary reactor stage (e.g., WGS) or by optimizing catalysts or operating conditions. 

20 to 40 bar (if the pressure is too low, additional energy is needed to compress outlet gases) and takes place according to the following basic reaction  

After the reforming reaction, the gas is quickly cooled down to about 350 450 °C before it enters the (high-temperature) water-gas shift reaction (CO shift). Here, the exothermic catalytic conversion takes place of the carbon monoxide formed with steam to hydrogen (H2) and carbon dioxide (C02) in the following reaction  

The gas purity demanded determines the extent of the gas treatment necessary. In the case of deliberate C02 separation with subsequent storage, the C02 can be 

Decentralised hydrogen production from natural gas for onsite applications (fuel cells, refuelling stations for hydrogen vehicles) eliminates or reduces the problems of distribution and storage. Nevertheless, current technology has high costs because it lacks economy of scale. Lower pressure and temperature and lower-cost materials are 

5 To reach a better CO conversion, it is possible to add a low-temperature shift reactor, which increases the CO2 capture rate (see also Fig. 10.3). If both clean CO2 for storage and clean hydrogen for fuel cell applications are required, a combination of a C02-capture plant (e.g., absorption with Rectisol) and a PSA plant is necessary. If only pure hydrogen is required, a PSA unit would be sufficient (and is standard practice), but the C02 stream would be contaminated by impurities, such as H2, N2 or CO, which have to be removed for geological storage. 

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Coal gasification technology dates to the early nineteenth century but has been largely replaced by natural gas and oil. A more hydrogen-rich synthesis gas is produced at a lower capital investment. Steam reforming of natural gas is appHed widely on an iadustrial scale (9,10) and ia particular for the production of hydrogen (qv). 

Synthesis Gas Chemicals. Hydrocarbons are used to generate synthesis gas, a mixture of carbon monoxide and hydrogen, for conversion to other chemicals. The primary chemical made from synthesis gas is methanol, though acetic acid and acetic anhydride are also made by this route. Carbon monoxide (qv) is produced by partial oxidation of hydrocarbons or by the catalytic steam reforming of natural gas. About 96% of synthesis gas is made by steam reforming, followed by the water gas shift reaction to give the desired H2 /CO ratio. 

Higher range based on a 2.8 X 10 m /d steam reformer of natural gas at 1.90/kJ. Cost varies based on volume deflvered. 

High temperature steam reforming of natural gas accounts for 97% of the hydrogen used for ammonia synthesis in the United States. Hydrogen requirement for ammonia synthesis is about 336 m /t of ammonia produced for a typical 1000 t/d ammonia plant. The near-term demand for ammonia remains stagnant. Methanol production requires 560 m of hydrogen for each ton produced, based on a 2500-t/d methanol plant. Methanol demand is expected to increase in response to an increased use of the fuel—oxygenate methyl /-butyl ether (MTBE). 

Steam Reformings of Natural Gas. This route accounts for at least 80% of the world s methanol capacity. A steam reformer is essentially a process furnace in which the endothermic heat of reaction is provided by firing across tubes filled with a nickel-based catalyst through which the reactants flow. Several mechanical variants are available (see Ammonia). 

In the catalytic steam reforming of natural gas (see Fig. 2), the hydrocarbon stream, principally methane, is desulfurized and, through the use of superheated steam (qv), contacts a nickel catalyst in the primary reformer at ca 3.04 MPa (30 atm) pressure and 800°C to convert methane to H2. 

Based on these developments, the foreseeable future sources of ammonia synthesis gas are expected to be mainly from steam reforming of natural gas, supplemented by associated gas from oil production, and hydrogen rich off-gases (especially from methanol plants). 

A major route for producing synthesis gas is the steam reforming of natural gas over a promoted nickel catalyst at about 800°C ... 

The steam reforming of natural gas process is the most economic near-term process among the conventional processes. On the other hand, the steam reforming natural gas process consists of reacting methane with steam to produce CO and H2. The CO is further reacted or shifted with steam to form additional hydrogen and CO2. The CO2 is then removed from the gas mixture to produce a clean stream of hydrogen. Normally the CO2 is vented into the atmosphere. For decarbonization, the CO2 must be sequestered[l,2]. The alternative method for hydrogen production with sequestration of carbon is the thermal decomposition of methane. 

Nuclear energy can produce hydrogen in several ways (1) nuclear heated steam reforming of natural gas, (2) electrolysis of water using nuclear power, (3) HTE using minor heat and major electricity from nuclear reactor, and (4) thermochemical splitting of water using... 

Table 7.18. Input and output data for the production of hydrogen via onsite steam reforming of natural gas ...

Until around 2030, steam reforming of natural gas plays a role for central production (with CCS), but in the long term this option becomes less attractive owing to the assumed increase of gas prices. 

Steam reforming of natural gas plus addition of CO2 to adjust the C0 H2 ratio to 1 2... 

Hydrogen production from fossil fuels is based on steam reforming of natural gas, thermal cracking of natmal gas, partial oxidation of heavier than naphtha... 

Today the two most common methods used to produce hydrogen are (1) steam reforming of natural gas, and (2) electrolysis of water. The predominant method for producing synthesis gas is steam reforming of natural gas, although other hydrocarbons can be used as feedstocks. For example, hydrogen can be produced from the biomass reforming process. 

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