GAS BURNER WITH A PREMIXING/PREHEATING ZONE

Abstract: Mixing and heating device in a gas burner com­ prising a housing (1) having a gas inlet (2a, 2b) to which a supply for gaseous fuel and oxidant are connected, a gas outlet (3) communicating with the burner, a preheating/pre­ mixing zone (c) filled with particulate matter and extending between the gas inlet and the gas outlet. A plurality of heat exchange pipes (6) can be arranged in the premixing/preheating zone.

Description: The invention relates to a gas burner provided with a premixing/preheating zone for partial combustion of a gaseous fuel and an oxidant. In 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. Partial 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. In the reactor a flame is maintained in which the fuel reacts with oxygen-containing gas at high temperatures. The 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. The 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. Since 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. In 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. Preheating is, in particular, a problem for oxygen as materials applied do not allow preheating over 200-250 °C. As far as mixing is concerned this is mostly accomplished just before or beyond the mouth of the burner. Premixing within the burner is generally not carried out because of the danger of flashback and/or explosion. Thus, 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. It is another object of the invention to provide such a burner with low HCN formation and/or low or non soot gasification. Therefore, the invention provides a burner for partial oxidation of a gaseous fuel and an oxidant, comprising 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, characterized in that said housing is hollow and horizontal and is partially filled with a layer of loose particles which rest on a supporting structure within said housing, said loose particles extending between both the vertical end walls and the side walls of the cylinder, said layer performing the functions of pre-mixing the gases and a flame arrester, said inlet for the gaseous fuel and oxidant being arranged below said supporting structure and said gas outlet being arranged above said layer of particles. The 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. In this manner a good premixing is ensured whereas any onset of combustion is smothered. Further, the packing allows the installation of heat exchange surfaces for (further) preheating of the gas mixture. Advantageously, 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. It is remarked, that WO-A-8,606,155 discloses a burner where, apparently, the combustion gas is sent through a packing material before being combusted on the surface of the material together with air/an oxygen carrier which bypasses the material. However, this document does not suggest a solution to the problem of ensuring a good pre-mixing of an oxygen-containing gas and fuel without combustion as there is no pre-mixing. The 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. Advantageously, 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. Advantageously the particles can be either refractory or metallic. In this manner the porous burner will not develop fissures due to expansion etc. and very large capacity burners can thus be made.

Claims: A burner for partial oxidation of a gaseous fuel and an oxidant, comprising a housing (1) having a gas inlet (2a, 2b) to which a supply of gaseous fuel and oxidant are connected, said housing being further provided with a gas outlet (3) in communication with the burner, characterized in that said housing (1) is a hollow horizontal cylinder and is partially filled with a layer of loose particles which rest on a supporting structure within said housing (1), said loose particles extending between both the vertical end walls and the side walls of the cylinder, said layer performing the functions of pre-mixing the gases and a flame arrester, said inlet (2a, 2b) for the gaseous fuel and oxidant being arranged below said supporting structure (5) and said gas outlet (3) being arranged above said layer of particles. The burner as claimed in claim 1 characterized in that a plurality of heat exchange pipes (6) is arranged in the premixing and/or preheating zone. The burner as claimed in claims 1 or 2 characterized in that the inert packing consists of beads. The burner as claimed in claims 1 or 2 characterized in that the particles are refractory. The burner as claimed in claims 1 or 2 characterized in that the particles are metallic. The burner as claimed in claims 1 or 2 characterized in that the particles are sand. The burner as claimed in claim 5 characterized in that the particles are aluminium grains.

Inventors: VAN DER BURGT, MAARTEN JOHANNES
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1989
Main classification: F23D14
IPC codes: F23D14, C01B3