Gas burner with a premixing/preheating zone.

0001The invention relates to a gas burner provided with a premixing/preheating zone for partial combustion of a gaseous fuel and an oxidant.

0002In such a burner the fuel is introduced together with an oxygen-containing gas into a reactor space operating under appropriate pressure conditions for producing for example synthesis gas, fuel gas or reducing gas.

0003Partial combustion, also known as gasification, of a gaseous fuel is obtained by the reaction of the fuel with oxygen. The fuel contains as combustable components, mainly carbon and hydrogen, which react with the supplied oxygen - and possibly with any steam and carbon dioxide as may be present - to form carbon monoxide and hydrogen. At some temperatures it is also possible to form methane.

0004In the reactor a flame is maintained in which the fuel reacts with oxygen-containing gas at high temperatures.

0005The fuel is usually passed into the reactor via the burner, and the oxygen-containing gas is also passed via the burner into the reactor. In some processes a moderator gas such as steam or carbon dioxide is also passed via the burner to the reactor; such a moderator gas is often advantageous for controlling the gasification temperature.

0006The reactants can be introduced in any desired manner, e.g., horizontally or vertically, into the reaction zone of a conventional refractory lined partial oxidation gas generator, and in particular gasification apparatus can be provided with a plurality of burners for the reactants positioned on substantially opposite sides of the combustion zone, whereby the reactants are introduced horizontally and the burner jets impinge on each other to facilitate the partial oxidation process and to minimize erosion of the refractory wall.

0007Since flame temperatures may exceed 2000 °C or more, a primary concern of such burners is to prevent damage to the burner front, also referred to as the burner face, caused by the high heat flux during the gasification process. To protect the burner front from overheating, it has been suggested to provide a refractory lining applied to the outer surface of the burner front wall and/or provide a hollow wall member with internal cooling passages through which cooling fluid is circulated at a rapid rate.

0008In particular, the invention relates to a specific gas burner which is applied in gas-fired furnaces and gasifiers. In gas-fired furnaces and gasifiers reducing gases such as CO, H₂, hydrocarbons, and oxidizing gases such as air, O₂ have to be mixed and for an efficient operation preheating of these gases is often required.

0009Preheating is, in particular, a problem for oxygen as materials applied do not allow preheating over 200-250 °C.

0010As far as mixing is concerned this is mostly accomplished just before or beyond the mouth of the burner.

0011Premixing within the burner is generally not carried out because of the danger of flashback and/or explosion.

0012Thus, it is an object of the invention to provide a gas burner provided with a premixing/preheating zone to be used for partial combustion of a gaseous fuel and oxidant wherein explosive gas mixtures can be premixed and/or preheated prior to their partial combustion.

0013It is another object of the invention to provide such a burner with low HCN formation and/or low or non soot gasification.

0014Therefore, the invention provides a gas burner provided with a mixing and heating zone for partial oxidation of a gaseous fuel and an oxidant, characterized by a housing having a gas inlet to which a supply of gaseous fuel and oxidant are connected, said housing being further provided with a gas outlet in communication with the burner, said burner comprising a flame arresting zone and a premixing/preheating zone filled with porous particulate matter or packing material and extending between the gas inlet and the gas outlet.

0015The invention has been based upon the step of mixing the two reactants (gaseous fuel, oxidant) when relatively cold (i.e. well below their ignition temperature) and leading the gas mixture thus obtained through an inert packing. Advantageously, such an inert packing may consist of beads, raschig rings or wire mesh.

0016In this manner a good premixing is ensured whereas any onset of combustion is smothered.

0017Further, the packing allows the installation of heat exchange surfaces for (further) preheating of the gas mixture.

0018Advantageously, the device of the invention com­prises a shell and tube heat exchanger in which the gases are mixed and heated in a space filled with packing material, in which tubes are arranged through which heating medium is flowing.

0019The invention will now be described by way of example in more detail by reference to the accompanying drawing, in which the figure represents a view of an advantageous embodiment of the present invention. Referring to the figure a reactor for partial combustion consists of a housing 1 provided with a gas inlet (2a, 2b) for fuel (advantageously natural gas) and oxidant, and a gas outlet 3. Typical dimensions of such a reactor are as follows: length: 10 metres, and diameter: 5 metres. The reactor is provided with a reaction zone A, a flame arresting zone B and a pre­mixing and preheating zone C. The zones B and C are filled with a layer of particulate matter or packing material and extending between the said inlet and said outlet. Advantageously the reactor is a horizontal cylindrical vessel in which the porous or packing material consists of a layer of loose particles (for example sand or aluminium grains) which rest on a supporting structure 5 arranged in any manner suitable for the purpose in said reactor. The inner wall of the reactor is advantageously provided with an insulating refractory 4. Through the gas inlet a gaseous fuel (for example natural gas or methane) and an oxidant (for example oxygen-containing gas or oxygen) are supplied to the premixing zone C. In the zone C premixing of the fuel and oxidant takes place and subsequently the gaseous mixture is fed through the porous layer on the support grid 5 to the reaction zone A and the synthesis gas obtained is fed to the gas outlet 3.

0020Advantageously, preheating means such as a plural­ity of heat exchange pipes 6 can be arranged in any suitable manner in or below the packing material in the premixing zone. However, it will be appreciated that such heat exchange pipes are optional.

0021Advantageously the particles can be either refractory or metallic.

0022In this manner the porous burner will not develop fissures due to expansion etc. and very large capacity burners can thus be made.

0023Various modifications of the present invention will become apparent to those skilled in the art from the foregoing description. Such modifications are intended to fall within the scope of the appended claims.