Methane reformer
Encyclopedia
A methane refomer is a device based on steam reforming
or autothermal reforming and is a type of chemical synthesis
, which can produce pure hydrogen
gas from natural gas
using a catalyst. There are two natural gas reformer technologies — autothermal reforming (ATR) and steam methane reforming (SMR). Both methods work by exposing natural gas to a catalyst (usually nickel
) at high temperature and pressure.
(methane
) or refinery feedstock into hydrogen and carbon monoxide
(syngas). Syngas reacts further to give more hydrogen and carbon dioxide in the reactor. The carbon oxides are removed before use by means of pressure swing adsorption
(PSA) with molecular sieves for the final purification. The PSA works by absorbing all impurities from the syngas stream to leave a pure hydrogen gas.
. 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 reactions can be described in the following equations, using CO2:
And using steam:
The outlet temperature of the syngas is between 950-1100 C and outlet pressure can be as high as 100 bar
.
The main difference between SMR and ATR is that SMR uses no oxygen. The advantage of ATR is that the H2:CO can be varied, this is particularly useful for producing certain second generation biofuel
s, such as DME
which requires a 1:1 H2:CO ratio.
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Steam reforming
Fossil fuel reforming is a method of producing hydrogen or other useful products from fossil fuels such as natural gas. This is achieved in a processing device called a reformer which reacts steam at high temperature with the fossil fuel. The steam methane reformer is widely used in industry to...
or autothermal reforming and is a type of chemical synthesis
Chemical synthesis
In chemistry, chemical synthesis is purposeful execution of chemical reactions to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions...
, which can produce pure hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
gas from natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
using a catalyst. There are two natural gas reformer technologies — autothermal reforming (ATR) and steam methane reforming (SMR). Both methods work by exposing natural gas to a catalyst (usually nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
) at high temperature and pressure.
Steam reforming
Steam reforming (SR), sometimes referred to as steam methane reforming (SMR) uses an external source of hot gas to heat tubes in which a catalytic reaction takes place that converts steam and lighter hydrocarbons such as natural gasNatural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
(methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
) or refinery feedstock into hydrogen and carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
(syngas). Syngas reacts further to give more hydrogen and carbon dioxide in the reactor. The carbon oxides are removed before use by means of pressure swing adsorption
Pressure swing adsorption
Pressure swing adsorption is a technology used to separate some gas species from a mixture of gases under pressure according to the species' molecular characteristics and affinity for an adsorbent material. It operates at near-ambient temperatures and so differs from cryogenic distillation...
(PSA) with molecular sieves for the final purification. The PSA works by absorbing all impurities from the syngas stream to leave a pure hydrogen gas.
Autothermal reforming
Autothermal reforming (ATR) uses oxygen and carbon dioxide or steam in a reaction with methane to form syngasSyngas
Syngas is the name given to a gas mixture that contains varying amounts of carbon monoxide and hydrogen. Examples of production methods include steam reforming of natural gas or liquid hydrocarbons to produce hydrogen, the gasification of coal, biomass, and in some types of waste-to-energy...
. 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 reactions can be described in the following equations, using CO2:
- 2CH4 + O2 + CO2 → 3H2 + 3CO + H2O
And using steam:
- 4CH4 + O2 + 2H2O → 10H2 + 4CO
The outlet temperature of the syngas is between 950-1100 C and outlet pressure can be as high as 100 bar
Bar (unit)
The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...
.
The main difference between SMR and ATR is that SMR uses no oxygen. The advantage of ATR is that the H2:CO can be varied, this is particularly useful for producing certain second generation biofuel
Biofuel
Biofuel is a type of fuel whose energy is derived from biological carbon fixation. Biofuels include fuels derived from biomass conversion, as well as solid biomass, liquid fuels and various biogases...
s, such as DME
Dimethyl ether
Dimethyl ether , also known as methoxymethane, is the organic compound with the formula . The simplest ether, it is a colourless gas that is a useful precursor to other organic compounds and an aerosol propellant. When combusted, DME produces minimal soot and CO, though HC and NOx formation is...
which requires a 1:1 H2:CO ratio.
Advantages and disadvantages
The capital cost of steam reforming plants is prohibitive for small to medium size applications because the technology does not scale down well. Conventional steam reforming plants operate at pressures between 200 and 600 psi with outlet temperatures in the range of 815 to 925 °C. However, analyses have shown that even though it is more costly to construct, a well-designed SMR can produce hydrogen more cost-effectively than an ATR.See also
- Catalytic reformingCatalytic reformingCatalytic reforming is a chemical process used to convert petroleum refinery naphthas, typically having low octane ratings, into high-octane liquid products called reformates which are components of high-octane gasoline...
- Reformed methanol fuel cellReformed methanol fuel cellReformed Methanol Fuel Cell or Indirect Methanol Fuel Cell systems are a subcategory of proton-exchange fuel cells where, the fuel, methanol , is reformed, before being fed into the fuel cell...
- PROXPROXPROX is an acronym for PReferential OXidation, and refers to the preferential oxidation of a gas on a catalyst.The catalyser preferentially oxidises carbon monoxide using a heterogeneous catalyst placed upon a ceramic support...
- Partial oxidationPartial oxidationPartial oxidation is a type of chemical reaction. It occurs when a substoichiometric fuel-air mixture is partially combusted in a reformer, creating a hydrogen-rich syngas which can then be put to further use, for example in a fuel cell...
External links
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