A common misconception about natural gas is that it is running out quickly. In fact, there is a vast amount of natural gas estimated to still be in the ground. According to latest estimate of Energy Information Administration (EIA) of proved natural gas reserves, the total available future supply can be available for more than about 100 years of supply at current rates of consumption in the case of US alone. Natural Gas is one of the principle sources of energy for many of our day-to-day needs and activities.
Chemical composition of natural Gas
Component Range (mole %)
Methane 87 - 96
Ethane 1.5 - 5.1
Propane 0.1 - 1.5
iso – Butane 0.01 - 0.3
normal – Butane 0.01 - 0.3
iso – Pentane trace - 0.14
normal – Pentane trace - 0.04
Hexanes plus trace - 0.06
Nitrogen 0.7 - 5.6
Carbon Dioxide 0.1 - 1
Oxygen 0.01 - 0.1
Hydrogen trace - 0.02
Specific Gravity 0.57 - 0.62
Gross Heating Value (MJ/m3), dry basis: 36.0 - 40.2
Hydrogen can be generated from natural gas with approximately 80% efficiency and the steam reforming of methane or natural gas usually produces bulk hydrogen. The primary methods in which natural gas is converted to hydrogen are:
(1) reaction with either steam (steam reforming),
(2) oxygen (partial oxidation), or
(3) both in sequence (auto thermal reforming).
Steam-Methane Reforming
Steam reforming is a process in which high-temperature steam (700°C–1000°C) is used to produce hydrogen from natural gas. In steam reforming, methane reacts with steam under high pressure in the presence of a catalyst to produce hydrogen, carbon monoxide, and a relatively small amount of carbon dioxide. Heat is supplied for the reaction to proceed. In the second stage carbon monoxide and steam are reacted using a catalyst to produce carbon dioxide and more hydrogen. Carbon dioxide and other impurities are removed from the gas stream, leaving essentially pure hydrogen using pressure-swing adsorption.
Partial Oxidation
In Partial oxidation process methane in natural gas reacts with oxygen in air to form hydrogen in a bed of catalyst. This commercial process route is basically the result of sequential combustion reactions in which the gas is burnt with deficit oxygen (nearly 30 % of stoichiometric requirement). Depending on the feed -stock the product gas may require purification of sulphur compounds and CO2 - removal. The advantage of dispensing with an external heat source favours the partial oxidation step, since the oxidation of CO supplies the necessary heat. Partial oxidation is an exothermic process—it gives off heat. The process is, typically, much faster than steam reforming and requires a smaller reactor vessel. As can be seen from the chemical reactions of partial oxidation (below), this process initially produces less hydrogen per unit of the input fuel than is obtained by steam reforming of the same fuel.
Auto thermal reforming (ATR)
Auto thermal reforming (ATR) uses oxygen and carbon dioxide or steam in a reaction with methane. Auto thermal reactor concepts for the heat integrated coupling of endothermic and exothermic reactions are required for an efficient on-site production of hydrogen from natural gas for use in fuel cells. The reaction takes place in a single chamber where the methane is partially oxidized. The reaction is exothermic due to the oxidation. When the ATR uses carbon dioxide the H2: CO ratio produced is 1:1; when the ATR uses steam the H2: CO ratio produced is 2.5:1 The advantage of ATR is that the H2: CO can be varied, this is particularly useful for producing certain second-generation biofuels.
Chemical composition of natural Gas
Component Range (mole %)
Methane 87 - 96
Ethane 1.5 - 5.1
Propane 0.1 - 1.5
iso – Butane 0.01 - 0.3
normal – Butane 0.01 - 0.3
iso – Pentane trace - 0.14
normal – Pentane trace - 0.04
Hexanes plus trace - 0.06
Nitrogen 0.7 - 5.6
Carbon Dioxide 0.1 - 1
Oxygen 0.01 - 0.1
Hydrogen trace - 0.02
Specific Gravity 0.57 - 0.62
Gross Heating Value (MJ/m3), dry basis: 36.0 - 40.2
Hydrogen can be generated from natural gas with approximately 80% efficiency and the steam reforming of methane or natural gas usually produces bulk hydrogen. The primary methods in which natural gas is converted to hydrogen are:
(1) reaction with either steam (steam reforming),
(2) oxygen (partial oxidation), or
(3) both in sequence (auto thermal reforming).
Steam-Methane Reforming
Steam reforming is a process in which high-temperature steam (700°C–1000°C) is used to produce hydrogen from natural gas. In steam reforming, methane reacts with steam under high pressure in the presence of a catalyst to produce hydrogen, carbon monoxide, and a relatively small amount of carbon dioxide. Heat is supplied for the reaction to proceed. In the second stage carbon monoxide and steam are reacted using a catalyst to produce carbon dioxide and more hydrogen. Carbon dioxide and other impurities are removed from the gas stream, leaving essentially pure hydrogen using pressure-swing adsorption.
Partial Oxidation
In Partial oxidation process methane in natural gas reacts with oxygen in air to form hydrogen in a bed of catalyst. This commercial process route is basically the result of sequential combustion reactions in which the gas is burnt with deficit oxygen (nearly 30 % of stoichiometric requirement). Depending on the feed -stock the product gas may require purification of sulphur compounds and CO2 - removal. The advantage of dispensing with an external heat source favours the partial oxidation step, since the oxidation of CO supplies the necessary heat. Partial oxidation is an exothermic process—it gives off heat. The process is, typically, much faster than steam reforming and requires a smaller reactor vessel. As can be seen from the chemical reactions of partial oxidation (below), this process initially produces less hydrogen per unit of the input fuel than is obtained by steam reforming of the same fuel.
Auto thermal reforming (ATR)
Auto thermal reforming (ATR) uses oxygen and carbon dioxide or steam in a reaction with methane. Auto thermal reactor concepts for the heat integrated coupling of endothermic and exothermic reactions are required for an efficient on-site production of hydrogen from natural gas for use in fuel cells. The reaction takes place in a single chamber where the methane is partially oxidized. The reaction is exothermic due to the oxidation. When the ATR uses carbon dioxide the H2: CO ratio produced is 1:1; when the ATR uses steam the H2: CO ratio produced is 2.5:1 The advantage of ATR is that the H2: CO can be varied, this is particularly useful for producing certain second-generation biofuels.
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