NL8104691A - PROCESS FOR THE PREPARATION OF A FREE PARTICLE-FREE SYNTHESIS GAS. - Google Patents

Description

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Short designation: Process for the preparation of a virtually particle-free synthesis gas.

The invention relates to a process for the preparation of carbon monoxide and hydrogen, ie synthesis gas, from solid carbonaceous fuels by partial oxidation with an oxygen-containing gas and the removal of the ash so produced. In particular, it relates to the gasification of solid carbonaceous fuels at superatmospheric pressure in a reactor of the non-catalytic jet type into which a solid fuel suspension in liquid phase water is introduced into a reaction zone which is at an autogenous temperature in the range about 983-1760 ° C, and reacting therewith with oxygen.

The development of carbon monoxide and hydrogen or synthesis gas by the non-catalytic reaction of solid carbonaceous fuel with air, oxygen-enriched air or relatively pure oxygen is known from U.S. Pat. No. 3,544,291. Partial oxidation of solid fuels, such as coal or petroleum coke, represents a very economical process for the production of synthesis gas 20 in large quantities. In the flow-type gasifier or partial oxidation reactor, solid fuel is reacted with an oxygen-containing gas in a closed compact reaction zone in the absence of packing at an autogenous temperature within the range of about 983-1760 ° C, at preferably at a temperature in the range of 1096-1538 ° C.

Usually, in the gasification of fuels such as coal or coke, the fuel in finely divided form is subjected to partial oxidation with the production of a product gas containing carbon monoxide and hydrogen and. which also contains small amounts of carbon dioxide and methane and, if the feed contains sulfur, also contains hydrogen sulfide and carbonyl sulfide.

There, however, because insufficient oxygen is led into the gasification zone for the complete combustion of the carbon in the fuel, i.e. for the conversion

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of all the carbon in the fuel in carbon dioxide, a small portion of the solid fuel passes through the gasification zone without being converted to an oxide of carbon. In addition, when the feed for the gasification zone contains ash, ash particles will also appear in the product gas.

Usually it is desirable to remove these solid particles from the product gas. For example, if the sensible heat of the gas is to be recovered by indirect heat exchange, it is recommended to remove the solid particles from the gas before it is led into a heat exchanger to prevent them from collecting on the walls 70 or heat transfer surfaces of the heat exchanger with subsequent disturbance of the flow of fluids therethrough and the transfer of heat. One way to do this is to collide the hot particles on the surface of water in a quench zone to quench them (cool rapidly) and moisten them, removing them from the gas stream and transferring them into the water . In another method, if the product gas is to be used for the preparation of hydrogen, the gas is usually quenched by passing it into water below its surface in a quench zone where the solid particles are retained in the water and the substantially particle-free gas saturated with water then subjected to catalytic exchange conversion. A combination of such techniques is described in U.S. Patent 3,998,609. In order to prevent build-up of solids and / or impurities in the quench water, part of the quench water is periodically or continuously removed and, in order to maintain a constant liquid level in the quench zone, replaced with water, preferably purified water which is recycled from an outlet zone 8104691 £ * - 3 - to which the removed part has been transferred.

If the gasifier is to operate at elevated pressure, the solid particles must be removed from the system without breaking the pressure and this can be done by passing the 5 particles into a sluice vessel and then releasing them from the system. Since the operation of the sluice vessel is controlled by valves, the inlet of the sluice vessel is generally of a relatively small diameter compared to the gasifier, meaning there is a portion of downwardly decreasing cross-sectional area immediately above the sluice vessel .

Unfortunately, there are cases where material balances show that for the amount of feed for the gasifier and the amount of gas produced, there is a shortage in the amount of solid particles removed by the sluice vessel. As this condition continues for an extended period of time, it becomes necessary to abort the operation and remove the blockage commonly found in the constricted portion of the device above the lock valve top valve.

An advantage of the invention is that it makes it possible to produce a virtually particle-free gas containing carbon monoxide and hydrogen. Another advantage is that the invention makes it possible to prepare synthesis gas under superatmospheric pressure. Yet another advantage is that the invention makes it possible to improve the removal of ash and unreacted solid fuel particles from a system for the gasification of ash-containing fuels.

According to the invention there is provided a process for the preparation of substantially particle-free synthesis gas comprising subjecting an ash-containing fuel to partial oxidation under superatmospheric pressure to prepare a stream of synthesis gas containing carbon monoxide and hydrogen and hot particles consisting of ash and unreacted fuel quenching the hot particles by contacting them with water in a quenching zone, allowing the particles to deposit through this quenching zone in a water-filled collection zone and maintaining a flow of water containing quenched particles from this quenching zone to the said collection area, 8104691 V * - 4 -

The feed of the process of the invention includes any ash containing carbonaceous fuel such as coal, subbituminous coal, lignite, some types of coke, biomass and the like. Usually such a fuel is solid, although fuels which are liquid at elevated temperatures, such as coal liquefaction residue, can also be used. In order to be considered as ash-containing, the fuel must have an ash content of at least 1% by weight. If the feed has melted at elevated temperature, it can be preheated and introduced as a liquid into the gasification zone. However, if the fuel is solid at elevated temperatures, it should be ground to a particle size of less than 0.62 cm and preferably ground such that at least 95% by a U.S. standard 14 mesh sieve 15 (1.41 mm opening). The fuel is then injected into the gas developing zone where it is subjected to partial oxidation with a gas such as air, oxygen-enriched air, or substantially pure oxygen, ie oxygen of at least about 9.5% purity. The solid fuel can be introduced into the partial oxidation zone as a suspension in a liquid such as water or oil, or as a suspension in a gaseous or vaporous medium such as steam, carbon dioxide or mixtures thereof. Water or steam can also be introduced into the gasification or partial • oxidation zone as a temperature moderator when the fuel feed is liquid or a suspension of solids in oil or other flammable liquid.

In the gas development zone, the fuel is subjected to partial oxidation at an autogenous temperature of between 983-1760 ° C, preferably between about 1096-1538 ° C. The pressure in the gas development zone can vary between about 2.8-210 kg / cm, preferably between about 4.2-175 kg / cm. The oxygen can be introduced into the gasification zone in an atomic ratio of oxygen to carbon of between about 0.7 and 1.6, preferably between 0.8 and 1.2. If the fuel is solid and introduced into the gasification zone as a slurry in water, the slurry should contain less than about 50 wt% water, since a water content above this amount will affect the thermal efficiency of the reaction 8104591-5-5r * to influence.

In a process for recovering heat from synthesis gas prepared by partial oxidation of an ash-containing fuel, the gas may be passed downward from the gas developer through a radiation cooling zone along with the entrained ash particles or unreacted fuel particles present. The gas is then diverted from its original path by the radiation cooling zone and, in

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a preferred embodiment, in a more or less upward direction, through a convection cooling zone in which it is fed upwardly in indirect heat exchange with a cooling medium such as water. The solids pass on their way and come into contact with water in a quench zone at the base of the radiant cooling zone where they are wetted and tend to deposit in the water. The solids then pass downward through the top valve of a sluice vessel which can also be considered a deposit zone where they collect. Since the top valve of the sluice vessel is for the most part kept in open position, the sluice vessel is filled with water. Periodically, to drain the solids, the top valve of the sluice vessel is closed and a valve located on the bottom of the sluice vessel is opened to allow water and solids to drain from the system. When this is completed, the bottom valve of the sluice vessel is closed, the sluice vessel is filled with water, pressurized, and then the top valve is opened to allow additional ash or slag to deposit and collect in the sluice vessel. Alternatively and preferably as a corrosion preventive measure, the sluice vessel 30 is kept full of water while the collected solids are discharged. This is accomplished by preferably introducing water at the top of the sluice vessel, while the top valve between the sluice vessel and the quench chamber is closed, through a separate inlet at the same rate as the contents of the sluice vessel through the opened valve is let off. In this way, the sluice vessel is constantly full of water and air cannot enter the sluice vessel.

In order to prevent the formation of a blockage above the top valve of the sluice vessel, in one embodiment 8104691 * v i.

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of the invention, water is circulated externally from the sluice vessel to the quench zone to cause a downward flow of water containing entrained particles through the top valve valve of the sluice vessel. This can be accomplished by withdrawing water from the top or from near the top of the sluice vessel and returning it directly or indirectly to the quench zone. Due to a change in valves and conduits, the opening used to draw water back to the quench zone can be the same opening used to introduce water during the cycle of the sluice vessel annealing. Advantageously, the outlet for extracting water from the downward flowing stream of water containing quenched particles is separated by a baffle, so that a minimum of particles are returned to the quenching zone. By operating in this way, a continuous flow of water goes down from the quench zone to the y collection zone thereby assisting in transferring the solid material from the quench zone to the collection zone or sluice vessel and thereby avoiding the formation of a blockage. However, this flow is stopped when the sluice vessel cycle is started to remove the collected solid particles.

The flow rate of water from the quench zone to the collection zone or sluice vessel is not critical but should be greater than the spreading speed ie the speed of the upstream flow of water displaced by the descending ash particles if no circulation used to be. Practically, the downward flow rate should be at least 0.91 cm per second, preferably at least 1.52 cm per second.

Since the inlet and outlet of the sluice vessel are valve controlled, the connection between the outlet of the quench zone and the inlet to the sluice vessel has a portion of gradually decreasing cross-sectional area. To prevent larger particles of ash or slag from clogging this surface or blocking the valve, it is recommended to have a mill above the narrowed portion.

After the synthesis gas has left the convection section, it can be transferred for a convenient use such as for the synthesis of organic compounds, the preparation of hydrogen or for use as a fuel.

Although the radiant cooler has been described as a downflow cooler and the convection cooler as an upflow cooler, it is possible with changes in the appliance to allow the gas to flow through any part of the appliance in any direction.

In another way of heat recovery, the oxygen-containing gas and fuel is introduced into the generator or partial oxidation zone at its top and passed down the generator. A water-containing quench zone is located at the base of the generator, but before the hot gas product reaches the quench zone, it is directed in a more or less upward direction into a radiation cooling zone while the solids continue their path in the quench water where they are moistened and sink through the water in the quench zone into a sluice vessel or collection zone. The derivative gas can then be passed upward through a radiation cooling zone in one case and then down through a convection zone or in another case down through a radiation cooling zone and up through a convection cooling zone or alternatively both up or down through both cooling zones.

In addition, to assist in the movement of solid particles from the quench zone to the collection zone, water is circulated from the collection zone to the quench zone to provide a constant downward flow from the quench zone through the top valve of the sluice vessel to the collection zone. .

Water circulated outside of the collection zone can be introduced into the quench zone above the surface of the water contained therein and sprayed on the surface, thus serving to wet and float any floating particles on or on the other hand, it can be introduced below the surface of the quench water and directed upward towards the surface to improve turbulence in the quench zone or be directed downward increasing the force of the water flow to the sluice vessel and the tendency of slag or ash particles to be bridged over the narrower part of the lock barrel entrance resulting in blocking the flow of solids in the lock barrel or in combination of the three. When the circulating water

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is introduced below the surface of the quench water in an upward direction, a flotation effect is produced 5 which tends to separate the carbon-rich particles from denser ash-rich particles, then advantageously the quench blow-off is taken near the surface of the quench water to remove water that has a greater amount of carbon-rich particles. The quench blow-off stream is a stream that is removed from the quench zone to help reduce the amount of impurities, such as chlorides and formates in the quench water. A water supply is supplied into the quench zone to replace the water withdrawn in the quench blow-off, thereby keeping the water level in the quench zone nearly constant.

In another embodiment of the invention, rather than circulating water from the sluice vessel to the quench chamber, water can be withdrawn from the sluice vessel and combined with the quench blow-off stream and transferred to a deposition apparatus in which the solids settle out the water which can then be returned to the quench zone as make-up quench water or used for the preparation of additional suspension feed. To compensate for the increased flow of water to the deposition device, the flow of make-up quench water into the quench zone is increased in an amount equal to the amount taken from the sluice vessel. In this way, a flow of water from the quench chamber is maintained through the top valve of the sluice vessel into the sluice vessel 30.

A series of tests with the high-pressure gasification of coal, in which the feed for the gasifier is a Kentucky No. 9 coal, the efficacy of the method according to the. see the invention. All tests were performed under almost equal operating conditions. The first test lasted 26.6 hours when the operation had to be stopped due to slag bridging above the top valve of the sluice vessel.

After the bridge was removed, the gasification was resumed, but bridging with slag meant that the second test had to be stopped after 18 8104691 9 hours. The third run lasted 20.5 hours and the fourth run nearly 20 hours when each had to be discontinued for the same reasons. Prior to the fifth run, a vent system was installed to draw water from the top of the sluice vessel into the quench vent at a fixed rate. The downward flow of water from the quench chamber through the top valve of the sluice vessel into the sluice vessel at a rate of 2.13 cm per second was successful because the fifth test continued for 42.5 hours and was terminated not by slag clogging but by mechanical reasons.

When this condition was corrected, the unit was started up and ran successfully for 66.8 consecutive hours when the test was terminated voluntarily. Subsequently, the unit ran for 112 consecutive hours.

From the previous tests it is clear that before the installation according to the invention was used, it was necessary to stop the unit after about 20 to 25 hours of operation due to blockage. However, after the installation of a system that allowed water to flow from the quench chamber through the top valve of the sluice vessel into the sluice vessel, there was no clogging or bridging of slag in the installation and more than 200 hours were completed without encountering this problem .

While the invention has been described with respect to gasification systems in which the synthesis gas is introduced into the quench water below its surface so that not only the solid ash particles and unreacted fuel are quenched, but the synthesis gas itself is also quenched gasification operations in which the water in the quenching zone is in a more or less calm state.

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Claims (12)

1. Process for preparing a substantially particulate-free synthesis gas comprising subjecting an ash-containing fuel to partial oxidation under superatmospheric pressure to produce a stream of synthesis gas comprising carbon monoxide and hydrogen and hot particles of ash and unreacted fuel , quenching the particles by contacting them with water in a quenching zone, and allowing the quenched particles to deposit by said quenching zone in a water-filled collection zone, characterized by maintaining a quenched stream of water particles from said quench zone to said collection zone. Method according to claim 1, characterized in that said flow is maintained by circulating water from said collection zone to said quench zone. Method according to claim 2, characterized in that the circulating water is led into the quenching zone above the surface of the water present therein. Method according to claim 2, characterized in that the circulating water is introduced into the quench zone below the surface of the water present therein. Method according to Claims 1 to 4, characterized in that the gases and entrained particles exiting the partial oxidation zone pass through a radiation cooling zone before the particles reach the quenching zone. Method according to any one of claims 1-4, characterized in that the gases are diverted to a radiation cooling zone 30 while the particles continue their way in water in a quenching zone. Method according to claim 5 or 6, characterized in that the path of the gas through said radiation cooling zone is in a downward direction. Method according to claim 5 or 6, characterized in that the path of the gas through said radiation cooling zone is in an upward direction. Method according to any one of claims 1-8, characterized in that the collection zone is kept full of water 8104691, -u - while the particles are removed therefrom. 10. Method according to claim 1, characterized in that water withdrawn from the collection zone is combined with a blow-off stream extracted from the quenching zone, the so-formed mixture is allowed to deposit, and water which is removed from the deposition zone recovered back to the system. Method according to claim 10, characterized in that the water is returned from the deposition zone to the quench zone. Method according to claim 10, characterized in that the water is introduced from the deposition zone into the partial oxidation zone with the ash-containing feed. 8104691