The present invention relates to a burner for use in a partial-combustion process for producing synthesis gas from a finely divided solid fuel, such as pulverized coal. The invention further relates to a process for the partial combustion of a finely divided solid fuel, in which process such a burner is used.
The generation of synthesis gas is achieved by the partial combustion, also called gasification, of a hydrocarbonaceous fuel with free-oxygen at relatively high temperatures. It is well known to carry out the gasification in a reactor into which solid fuel and free-oxygen containing gas are introduced either separately or premixed at relatively high velocities. In the reactor a flame is maintained in which the fuel reacts with the free-oxygen at temperatures above 1000.degree. C. The solid fuel is normally passed together with a carrier gas to the reactor via a burner, while free-oxygen containing gas is introduced into the reactor via the same burner either separately or premixed with the solid fuel. Great care must be taken that the reactants are effectively mixed with one another. If the reactants are not brought into intimate contact with one another, the oxygen and solid fuel flow will follow at least partially independent trajectories inside the reactor. Since the reactor space is substantially filled with hot carbon monoxide and hydrogen, the oxygen will react rapidly with these gases and the very hot combustion products, carbon dioxide and steam, will follow independent trajectories having poor contact with the relatively cold solid fuel flow. This behavior of the oxygen will result in local hot spots in the reactor and may cause damage to the reactor refractory lining and increase the temperature surrounding the burner.
In order to attain a sufficient mixing of solid fuel with oxygen it has already been proposed to mix the fuel and oxygen in or upstream of the burner prior to introducing the fuel into a reactor zone. This has the disadvantage in that, especially at high pressure gasification, the design and operation of the burner are highly critical. The reason for this is that the time elapsing between the moment of mixing and the moment the fuel/oxygen mixture enters into the reactor zone must be invariably shorter than the combustion induction time of the mixture. The combustion time, however, shortens at a rise in gasification pressure. If the burner is operated at a low fuel load or, in other words, if the velocity of the fuel/oxygen mixture in the burner is low, the combustion induction time may be easily reached in the burner itself, resulting in overheating with the risk of severe damage to the burner.
The above problem of premature combustion in the burner itself, might be overcome by mixing the fuel and oxygen outside the burner in the reactor zone itself. In the latter case, special measures should be taken to ensure as good mixing of fuel and oxygen, necessary for a proper gasification. A drawback of mixing fuel and oxygen in the reactor itself outside the burner is, however, the risk of overheating of the burner front due to the hot flame caused by premature contact of oxygen with already formed carbon monoxide and hydrogen in the reactor. To promote a uniform mixing of fuel and oxygen, it is known to introduce the oxygen as high velocity jets into the fuel zone. Such high velocity jets, however, entrain the reactor gases rapidly. The higher the oxygen jet velocities, the more pronounced will be the contact of oxygen with already formed reactor gases. Entrainment of reactor gases by the oxygen jets along the burner may further cause damage to the burner front due to overheating caused said gas flows.