Compositions – Gaseous compositions
Patent
1998-08-07
2000-12-12
Griffin, Steven P.
Compositions
Gaseous compositions
252373, 252374, 252375, 252376, 252377, 423210, C10J 100, B01D 4700
Patent
active
061593958
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process and plant for reforming hydrocarbonaceous feedstocks.
Methanol is synthesised in large volumes annually by conversion of a carbonaceous feedstock, usually a hydrocarbonaceous feedstock such as natural gas, into a mixture of carbon oxides and hydrogen. Such a mixture of gases is often referred to as synthesis gas.
The conversion of a hydrocarbon-containing feedstock, such as natural gas, into synthesis gas can be effected by steam reforming.
In a conventional steam reforming process a mixture of desulphurised hydrocarbon feedstock, such as natural gas, and steam is passed at high temperature, typically a temperature of from about 600.degree. C. to about 1000.degree. C., and elevated pressure, typically from about 10 bar up to about 50 bar, over a suitable reforming catalyst, such as a supported nickel catalyst. One commercially recommended catalyst which can be used for this purpose uses a mixture of calcium and aluminium oxides as support for the nickel. When natural gas is the feedstock, the principal reaction is:
The reaction products themselves are further subject to the reversible "water gas shift" reaction in which carbon dioxide and hydrogen are produced from carbon monoxide and steam:
A number of different types of reformer are known in the art. One such type is known as a "compact reformer" and is described in WO-A-94/29013, which discloses a compact endothermic reaction apparatus in which a plurality of metallic reaction tubes are close-packed inside a reformer vessel. Fuel is burned inside the vessel, which comprises air and fuel distribution means to avoid excessive localised heating of the reaction tubes. In a compact reformer of this type heat is transferred from the flue gas vent and from the reformed gas vent of the reformer to incoming feedstock, fuel and combustion air. Other types of reformer are not as efficient as the compact reformer in transferring heat in this way. However, many other reformer designs are known and some are described in EP-A-0033128, U.S. Pat. No. 3,531,263, U.S. Pat. No. 3,215,502, U.S. Pat. No. 3,909,299, U.S. Pat. No. 4,098,588, U.S. Pat. No. 4,692,306, U.S. Pat. No. 4,861,348, U.S. Pat. No. 4,849,187, U.S. Pat. No. 4,909,808, U.S. Pat. No. 4,423,022, U.S. Pat. No. 5,106,590 and U.S. Pat. No. 5,264,008.
In a compact reformer of the type described in WO-A-94/29013 a hydrocarbonaceous feedstock is saturated with water and preheated before entering the reaction tubes.
Fuel is burned inside the compact reformer vessel, supplying radiant and convective heat to the reaction tubes, thereby raising the temperature of the process gas inside the tubes to reforming temperatures (e.g. from about 600.degree. C. to about 1000.degree. C.). A reforming catalyst is charged to the tubes in this region. As the reformed gas reaches the exit end of the catalyst its temperature is from about 700.degree. C. to about 1000.degree. C. This gas must be cooled before downstream methanol synthesis, which desirably is conducted at a temperature below about 300.degree. C.
In the compact reformer, combustion air supplied to the reformer is used to cool the reformed gas in the reaction tubes. Upon being cooled from, say, 850.degree. C. to 400.degree. C. the reformed gas passes through the Boudouard region at which dusting of the metal reformer tubes with carbonaceous deposits can occur according to the equation:
To avoid such metal dusting it is important, inter alia, to obtain the correct heat balance between the cooling combustion air and the reformed gas. A number of methods of achieving this balance are known in the art. One commercial method is to supply a larger quantity of air than is needed for combustion inside the reformer vessel. The extra mass of air cools the hot reformed gas to the desired temperature. However, this method has cost disadvantages because of the size of compressor needed to pump the excess air into the reformer. Another method is to cool the air supplied to the reformer but this is also expensive to achieve. Yet another method invol
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International Search Report, PCT/GB97/03417, Jun. 4, 1998 (4 pages).
Early Simon Robert
Gamlin Timothy Douglas
Linthwaite Mark Andrew
Griffin Steven P.
Kvaerner Process Technology Limited
Nave Eileen E.
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