Patent Application
20150075072
The present non-provisional patent application claims the benefit of priority from German Patent Application No. 102013218830.7, filed Sep. 19, 2013, the entire contents of which are incorporated herein by reference.
Divided central tube of a combined quenching and scrubbing system for an entrained flow gasification reactor
The invention relates to a combined quenching and scrubbing system for the cooling and cleaning of crude gases from an entrained flow gasification plant, in which fuel dusts are reacted with oxygen and moderators such as steam or carbon dioxide at temperatures between 1200-1900° C. and pressures up to 10 MPa to give a crude gas rich in CO and H2.
Fuel dusts are understood to mean finely ground coals of different carbonization level, dusts formed from biomasses, products of thermal pre-treatment, such as cokes, torrefaction products and fractions having high calorific values from communal and commercial residual and waste materials. The fuel dusts can be supplied to the gasification as a gas/solid or liquid/solid suspension. The gasification reactors can be provided with a cooling screen or with a refractory lining, as shown by the patent documents DE 4446803 and EP 0677567. In various systems introduced in industry, crude gas and the molten slag can be discharged separately or together from the reaction space of the gasification apparatus, as described, for example, in DE 19718131.
Entrained flow gasification, because of the fuel particles ground to a dust and short reaction times in the gasification space, causes an elevated dust content in the crude gas. Depending on the reactivity of the fuel, this entrained dust consists of soot, unconverted fuel particles and fine particles of slag and ash. The size varies between coarse particles having diameters greater than 0.5 mm and fine particles having a diameter down to 0.1 μm. The separability of the particles from the crude gas depends on this diameter, but also on the composition thereof. In principle, a distinction can be made between soot and ash or slag particles, soot particles generally being smaller and more difficult to separate from the crude gas. Slag particles have a higher density and hence better separability but, in contrast, have a higher hardness and hence erosive action. This leads to increased wear in the separators and crude gas-conducting lines, and can cause safety-relevant leaks and lifetime restrictions. For the removal of the dusts resulting from the fuels, various scrubbing systems are being used.
The prior art to date is described in patent document DE 102005041930 and in “Die Veredlung von Kohle” [The Addition of Value to Coal], DGMK, Hamburg, December 2008, Schingnitz, chapter on “GSP-Verfahren” [GSP Processes]. According to this, the crude gasification gas leaves the gasification space together with the slag formed from the fuel ash at temperatures of 1200-1900° C. and is cooled in a downstream quench space by injection of excess water and freed of the slag and, to a small extent, of entrained dust, it being possible for the quench space to be configured as a cavity quencher or provided with a crude gas-conducting central tube. A cavity quench system is disclosed, for example, in DE 102007042543, in which the crude gas that leaves the gasification space is sprayed with water and drawn off in the lower section beneath a roof construction.
DE 102006031816 exhibits a clear quench space entirely without internals, with injection of quenching water at one or more levels in such an amount that the crude gas is cooled and saturated with steam, and the excess quenching water is drawn off in the lower section alone or together with deposited slag. Variants with a central tube are disclosed by the patents DE 19952754, in which the central tube takes the form of a Venturi tube, DD 145860, in which the crude gas at the end of the central tube is subjected to additional scrubbing in the form of an airlift pump, and DD 265051, where elements for distribution of the crude gas flowing out at the end of the central tube are supposed to ensure uniform flow outward. CN 101003754 B describes an immersed quenching apparatus with a central tube, in which the hot crude gas from the gasification reactor is conducted together with the likewise hot slag downward into a water bath and flows upward as a gas/water suspension within the annular gap of the guide tube, which takes the form of a double tube. The gas/water separation takes place at the upper end of the guide tube. The gas/water suspension which flows upward in the annular gap is said to protect the inner central tube from overheating.
The solution according to patent document DE 102007042543 has the disadvantage that the cavity, as a result of pipelines of relatively high diameter for the removal of crude gas and the roof construction, offers deposition surfaces for entrained slags and dusts, which, as experience has shown, leads to blockages. DE 102006031816 requires homogeneous flow of the hot crude gas out of the gasification space, because there could otherwise be the risk of thermal overloading of the pressure-bearing vessel walls. The arrangement of a Venturi tube according to DE 19952754 can lead to unwanted variations in pressure in the gasification space, and these can barely be compensated for by means of control technology because of their short duration of action. Internals in the quench space and scrub space, as in the patents DD 265051 and DD 224045, can lead, as a result of the puzzolanic properties particularly of the fine dust components in the case of particular coal and ash types, to accumulating deposits having the strength of cement, which likewise lead to blockages and to an increase in pressure drop. This risk likewise exists in the solution according to CN 101003754 B. Should the gap between the inner and outer tubes of the central tube become blocked, the hot crude gas will flow downward in the uncooled inner tube, which can lead to the thermal destruction thereof and additionally endangers the pressure casing of the quench space as a result of overheating.
The problem addressed by the invention is that of providing a quenching and scrubbing system in which the hot gasification gas fed in on the input side and the entrained liquid slag firstly undergoes cooling with simultaneous deposition of particles, such as slag and dust, and the crude gas that leaves the quenching and scrubbing system on the output side secondly has an elevated hydrogen content.
This object is achieved by a crude gas scrubbing system disclosed herein.
In the inventive combined quenching and scrubbing system for cooling of the hot gasification gas and the entrained liquid slag, involving multistage cooling of the crude gas and contacting of the crude gas with quenching water, the conversion reaction that proceeds between carbon monoxide and steam provides an increased hydrogen content in the crude gas in conjunction with a substantial separation of particles out of the crude gas.
According to the invention, in addition to an injection of quenching and scrubbing water, the central tube is divided, the upper section receiving special configuration in the form of a tube wall which allows the additional cooling of the tube material. The central tube has, in the section facing the gas side, plating which protects the tube wall from corrosion, and the smooth surface prevents the caking of slag. Likewise in a particular configuration, nozzles are integrated through this tube wall, which enable the abovementioned supply of quenching and scrubbing water into the interior. The lower section of the central tube consists of smooth tube. Here, the cooling of crude gas and slag has advanced to such an extent that there is no risk of thermal overheating. At the end of the lower section, additional devices are provided, particularly for improvement of the scrubbing operation.
The invention is elucidated hereinafter by a working example, with reference to four figures. The figures show:
In the figures, identical designations denote identical elements.
In a gasification reactor 1 according to
As shown in
The nozzles for water injection 6 are conducted through the welded tube screen of the central tube upper section 11 via a nozzle aperture 17 of a particular construction according to
The width of the nozzle aperture 17 is configured such that it can be fitted into the distance between one winding and the third adjacent winding away from it in the wound tube screen. The nozzle aperture 17 has a central cylindrical seat 20 for a nozzle 6. Two parallel tube sections for separate guiding of the cooling water in two adjacent windings of the wound tube screen are conducted around the seat for the nozzle such that a cross-sectional constriction of the tube sections is substantially avoided. The avoidance of a cross-sectional constriction is brought about by virtue of the tube section, in the region where it is conducted around the seat for the nozzle, being narrower in one plane and correspondingly broader in the plane at right angles thereto. The nozzle aperture 17 is incorporated into the tube screen at the points 18 and 19, as a result of which cooling water flow is possible. The nozzle 6 is inserted into a water-cooled ring 20 and sealed tight via a flange connection 22.
A connecting element construction serves as a guide for the central tube lower section 12 in axial direction, in order to enable thermal expansion. For this purpose, eight connecting elements 31 are welded to the inner wall of the pressure casing of the quencher 5 and a ring 32 which guides the central tube lower section and can absorb radial forces.
Between the central tube lower section 12 and the pressure casing of the quencher 5, a lower guide tube 21 is connected to the connecting element construction such that the exiting crude gas flows upward in the annular space or gap 9 formed as a bubble column 8 and forms a secondary cooling and scrubbing stage. The lower end of the lower guide tube 21 is disposed at a lower level than the lower end of the central tube lower section 12, such that the crude gas ascends in the annular gap 9 as bubble column 8. The upper end of the lower guide tube 21 is disposed at a lower level than the surface of the water bath 7. Water entrained from the bubble column 8 in the annular gap 9 flows downward in the annular gap between the lower guide tube 21 and pressure casing of the quencher 5, forming a circuit. Particles which are entrained from the water flowing downward are separated out toward the slag discharge 10.
Referring to
The bubble column 8 which forms in the annular gap 9 constitutes a second cooling and scrubbing stage. A surface body disposed in the annular gap, by virtue of its angled metal sheets, brings about a restriction in the bubble size, as a result of which the contact between ascending crude gas and water bath 7 is improved, which increases the deposition level of particles entrained in the crude gas into the water bath. The deposition level is increased further when the angled metal sheets are arranged offset with respect to one another in different planes. To enhance the scrubbing effect, surface bodies 23 might be arranged in three different horizontal planes.
The crude gas which flows upward in the cavity 25 downstream of the annular gap 9 is contacted with further water through one or more nozzle ring(s) 26 as the third cooling and scrubbing stage, in order to continue the cleaning and remove further dust components. The nozzle ring 26 shown in
The steam-saturated crude gas at 200-220° C. leaves the quenching and scrubbing apparatus 5 via the crude gas outlet 27 for further treatment. The excess quenching water is removed in a controlled manner from the water bath 7 via the discharge 28, in order to be able to maintain the required water level. The excess water is cleaned and fed back again in the circuit.
The invention also comprises an apparatus for a combined quenching and scrubbing system for the cooling and cleaning of crude gases from an entrained flow gasification plant, in which hot crude gas and liquid slag from the gas and slag outlet 3 are passed in a water-filled central tube 4 into a water bath 7, in which the central tube 4 is divided into two, wherein the central tube upper section 11 takes the form of a tube screen and undergoes direct cooling, and the central tube lower section 12 transfers the precooled gas and the precooled slag into the water bath 7, forming a bubble column 8.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102013218830.7 | Sep 2013 | DE | national |
