Coal gasification reactor

Abstract: The slagging efficiency of a coal gasification process is increased to 90% by tangential firing at small angles and the installation of a stack of specific length over diameter ratio between the reactor outlet and the quench inlet. In this manner slag lifting and slag entrainment at the quench inlet - stack outlet are prevented.

Description: The present invention relates to a reactor for carrying out a partial oxidation process of a finely divided solid carbon-containing fuel and an oxidant. Finely divided solid carbon-containing fuels are applied in processes for the preparation of synthesis gas by the partial combustion of a finely divided solid carbon-containing fuel with an oxygen-containing gas in a reactor wherein liquid slag formed during the partial combustion process is removed through an outlet in the bottom of the reactor and passed by gravity through a slag discharge means into a water bath or slag quenching vessel where it is solidified by quenching. The partial combustion of finely divided solid carbon-containing fuel with substantially pure oxygen as oxygen-containing gas yields synthesis gas mainly consisting of carbon monoxide and hydrogen. When the oxygen-containing gas is air or oxygen-enriched air, the synthesis gas formed of course also contains a substantial quantity of nitrogen. By finely divided solid carbon-containing fuel is generally meant coal or another solid fuel, such as brown coal, peat, wood, coke, soot etc., but mixtures of liquid or gas and particulate solid fuels, are also possible. Advantageously, a moderator is also introduced into the reactor. The object of the moderator is to exercise a moderating effect on the temperature on the reactor. This is ensured by endothermic reaction between the moderator and the reactants and/or products of the synthesis gas preparation. Suitable moderators are steam and carbon dioxide. The gasification is advantageously carried out at a temperature in the range from 1200 to 1700 °C and at a pressure in the range from 1 to 200 bar. The reactor in which the preparation of synthesis gas takes place may have any suitable shape. The supply of finely divided solid carbon-containing fuel and oxygen-containing gas to the reactor can take place in any manner suitable for the purpose and will not be described in detail. Liquid slag formed in the partial combustion reaction drops down and is drained through the outlet located in the reactor bottom. In partial oxidation processes of finely divided solid carbon-containing fuels, such as for example coal gasification, the fuel is fed from a supply device to a gasifier by means of a suitable carrier fluid. The hot product gas usually contains sticky particles which lose their stickiness upon cooling. The sticky particles in the hot product gas will cause problems in the plant where the product gas is further processed, since undesirable deposits of the particles on, for example, walls, valves or outlets will adversely affect the process. Moreover, such deposits are very hard to remove. The sticky particles may be partly or completely in the molten state; they may comprise metals, salts or ashes, and, in general, these particles lose their stickiness at a temperature below about 800 °C. Therefore, the hot product gas is quenched in a quench section which is located above the product outlet on top of the reactor. In the quench section a suitable quench medium such as for example water or a gas is introduced into the product gas in order to cool the product gas. It is known to apply tangentially fired burners in partial oxidation processes of finely divided solid carbon-containing fuels, i.e. a plurality of tangentially directed burners are located on the same horizontal level at circumferential spaced points of the wall of the reactor vessel and cause vortex flow in the reactor. It has now appeared, however, that present reactor designs still have some disadvantages: the slagging efficiency is rather small (40-50%); there is a possibility for slag lifting to occur at the reactor outlet and short-circuiting of hot synthesis gas out of the reactor into the quench may occur. It is an object of the invention to provide a reactor design which has a slagging efficiency of 90-95%. It is another object of the invention to provide a reactor design wherein slag lifting and slag droplet entrainment is prevented. It is still another object of the invention to provide a reactor design wherein said short-circuiting of synthesis gas is prevented. The invention therefore provides a reactor for preventing slag lifting at the reactor top outlet and preventing slag droplets entrainment in the product gas in an exothermic partial oxidation process of a finely divided solid carbon-containing fuel and an oxidant, said reactor comprising a reactor vessel having an outlet for the product gas at its top, a slag outlet at its bottom, a plurality of burner openings in its side wall, a plurality of tangentially directed burners located on the same horizontal level at circumferential spaced points, with a specific firing angle, the reactor being provided with a quench above its outlet, characterized in that the reactor at its top outlet is connected to an extended pipe or stack, located between the reactor outlet and the quench inlet, and wherein on the lower part of said stack most of the slag leaving the said top outlet of the reactor during the partial oxidation process, will be deposited, said stack having a diameter which is considerably narrower than the diameter of the reactor and wherein the stack has a length-to-diameter ratio in the range of 4 to 6 and wherein the firing angle is greater than 0 degrees. It can be remarked that GB-A-718,410 discloses a reactor for carrying out the partial oxidation of pulverized coal in a two-step combination process of exothermic and endothermic reactions in a primary reaction chamber and a secondary reaction chamber. In the second reaction chamber the production of synthesis gas is completed. However, the above "slagging efficiency" problem and its specific prevention solution of the invention are not known from this document and cannot be derived therefrom. The term firing angle is defined as the angle between the symmetry axis of the burner jet and the line through the centre of the burner and the centre of the reactor at the same horizontal level. The invention will now be described by way of example in more detail by reference to the accompanying drawings, in which: fig. 1 represents schematically a longitudinal section of a conventional reactor and quench section; fig. 2 represents schematically a longitudinal section of a reactor design of the invention; fig. 3a represents a cross-section along the lines I-I of fig. 1, and fig. 3b represents a cross-section along the lines II-II of fig. 2. Referring now to fig. 1, a reactor vessel 1 has been shown. The reactor vessel 1 is provided with a slag outlet 2 at its bottom, a plurality of tangentially fired burners 3, a gas outlet 4 at its top and a quench system 5 comprising a quench inlet 5a above the reactor outlet 4. The tangentially directed burners 3 are located on the same horizontal level at circumferental spaced points and cause vortex flow in the reactor vessel 1. The quench system 5 is at its outlet 6 connected to equipment for further treating the synthesis gas. Such equipment is known to those skilled in the art and will not be described in detail. In fig. 2 the same reference numerals have been used as in fig. 1. In fig. 2 the reactor 1 is provided with an extended pipe or stack 4a at its outlet 4. This extension is located between the reactor outlet 4 and the quench inlet 5a and has a predetermined length-to-diameter ratio Ls/Ds. The quench system 5 is located remote from the reactor outlet. Ls/Ds is 4 to 6 and more in particular Ls/Ds is 5 (as shown in fig. 2). Further, in fig. 2, the quench system 5 has a length-to-diameter ratio Lq/Dq = 3 and the reactor 1 has a length-to-diameter ratio Lr/Dr = 3. Fig. 3a represents a tangential burner arrangement comprising 4 burners A, B, C, D. The burners are arranged horizontally and are directed to a central point E, which means that the firing angles are 0 degrees. Fig. 3b represents a tangential burner arrangement of the invention comprising 4 burners A', B', C', D' wherein the firing angles are 5 degrees. Advantageously, the firing angles according to the present invention are in the range of 3 to 5 degrees. The burners are directed to a central circle E′ having a determined area. When the reactor design of the invention is used, large centrifugal forces inside the stack will cause a large settling velocity and thus a large slagging efficiency, since most of the slag will be deposited in the lower part of the pipe extension, it is possible to decrease the swirl of the product gas by either installing cross hairs or by a further narrowing of the pipe. This will prevent cold syngas from re-entering the reactor. The stack will also reduce the turbulence of the syngas. This reduction and the fact that the stack wall immediately below the quench inlet is vertical and thus much steeper than the reactor roof in fig. 1 will be beneficial to prevent slag lifting or slag entrainment. Finally the stack will reduce flow short-circuiting. Thus the breakthrough times toward the reactor outlet increase. Consequently the conversion is enhanced and the outlet temperature may decrease. Various modifications of the present invention will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Such modifications are intended to fall within the scope of the appended claims.

Claims: A reactor for preventing slag lifting at the reactor top outlet and preventing slag droplets entrainment in the product gas in an exothermic partial oxidation process of a finely divided solid carbon-containing fuel and an oxidant, said reactor comprising a reactor vessel having an outlet for the product gas at its top, a slag outlet at its bottom, a plurality of burner openings in its side wall, a plurality of tangentially directed burners located on the same horizontal level at circumferential spaced points, with a specific firing angle, the reactor being provided with a quench above its outlet, characterized in that the reactor at its top outlet is connected to an extended pipe or stack, located between the reactor outlet and the quench inlet, and wherein on the lower part of said stack most of the slag leaving the said top outlet of the reactor during the partial oxidation process, will be deposited, said stack having a diameter which is considerably narrower than the diameter of the reactor and wherein the stack has a length-to-diameter ratio in the range of 4 to 6 and wherein the firing angle is greater than 0 degrees. The reactor as claimed in claim 1, wherein the stack has a length-to-diameter ratio of 5. The reactor as claimed in claim 1 or 2, wherein cross hairs for decreasing the swirl of the product gas are installed in the stack. The reactor as claimed in any one of claims 1-3, wherein the firing angle is 3 to 5 degrees.

Inventors: DAVERVELDT PETRUS H W M, HASENACK HENDRIKUS JOHANNES AN, DAVERVELDT, PETRUS H.W.M., HASENACK, HENDRIKUS JOHANNES ANTONIUS
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1990
Main classification: C10J3
IPC codes: C10J3