IE41619B1 - Coal gasification process with improved procedure for continuously discharging ash particles and apparatus therefor - Google Patents

Abstract

1495831 Removing ash from gasifiers KAMYR Inc 12 Feb 1975 [15 Feb 1974] 5958/75 Heading F4B A process for separating ash from pressurized synthetic gasifiers includes the steps of (i) confining the liquid within a first path 16 wherein the liquid is at a high pressure, by having a surface 12 communicating with the gas pressure at the ash particle discharge end of the gasifier 14, (ii) discharging ash particles into the high pressure liquid through the surface 12, (iii) maintaining a continuous flow of the liquid along a second path 18, at a pressure lower than that of the liquid in the first path, and (iv) continuously moving batches of liquid and entrained ash particles from the first path and adding the batches to a second path. The only liquid specified is water. Preferably the batchwise transfer of ash particles and water is performed using a cylindrical sluicing device 26 which includes a rotating wheel containing four diametric channels 74 arranged in two crossing pairs, each pair offset by 45 degrees from the other. Each channel may be rotated to communicate with an inlet 78 of a liner 76, the inlet being in permanent communication, through a hole in a housing 60, with the first, high pressure path 16, thereby filling the channel with ash and water. On rotation through 90 degrees (dashed lines in Fig. 1) the channel then communicates with the inlet 80 from the low pressure path 18 and water flow caused by pump 20 caused discharge of ash and water through sluicing device outlet 84 and then pipe 34. A temperature responsive valve 52 allows cold water to flow into the gasifier to prevent boiling of water in the gasifier and a throttle valve 56 bleeds water and ash from the high pressure path through channel 74 in response to increase in the level of the surface 12 to compensate for cold water input. A sieve 92 in an outlet 82 of the liner 76 allows flow to the throttle valve 56 but retains larger ash particles in the channel 74. Ash and water from valve 54 and pipe 34 fall on to a continuous foraminous belt 30 which retains ash and allows water to pass to a recycling tank 32 which supplies the pump 20 and a pump 38 which pumps water into the gasifier. In a further similar embodiment (Fig. 4, not shown), the gasifier incorporates a device to crush the ash (above or below the surface 12 of the water). Discharge through the sluice channel from the high pressure is recycled to the gasifier. Temperature is controlled by venting high pressure water, sieved free of ash, from the high pressure recycling line to the low pressure path in response to temperature; the level of the surface 12 is then maintained by cold water supplied in response to a fall in the level of the surface 12. In a final embodiment (Fig. 5, not shown) the high pressure outlet of the sluicing device is blocked by replacing the sieve 92 with a solid plate whereupon the channels of the sluicing device fill by gravity and leakage from the sluicing device. To control temperature, high pressure water is bled from the gasifier in response to the temperature of the water in the gasifier into the low pressure path, and cold water is supplied to the gasifier in response to lowering of the level of the surface 12. As a safety feature the raising of the level of the surface 12 is controlled by a further direct bleed from the high pressure gasifier water, which bleed is fed into the low pressure path when the level of the surface 12 exceeds a predetermined level.

Description

This invention relates to coal gasification and more particularly to a method and apparatus for removing ash, clinker, char and spent oil shale from a gasifier under pressure producing, for example, synthetic natural gas, water gas and producer gas. ' Known methods for discharging of ash particles from vessels under pressure usually involve intermittent operating procedures, the apparatus used consisting of a lock hopper where ash is charged at or near the vessel pressure.

The hopper charging port is then isolated from the vessel by a valving device and the hopper is vented to atmospheric pressure. The hopper discharging port is opened and the ash falls by gravity from the hopper. The next ash removal cycle is initiated by closing the hopper discharge port and pressurizing the hopper equally to the vessel pressure. Such known devices usually are provided with compressors and gas storage vessels to accomplish the venting and pressurizing cycles. Other more nearly continuous procedures involve the utilization of wheel charging apparatus such as star/conveyors and screw conveyors and are characterized by the charging of materials to the gasifier vessels at or near atmospheric pressure. These types of devices are practically incapable of transferring solid materials while containing large gas pressure differentials across their sealing surfaces. - 2 41619 An object of this invention is to provide a process which serves to improve the discharging of ash particles from known coal gasifiers by making the discharging continuous, to eliminate hopper venting and pressurizing cycles, and to provide a liquid seal volume to prevent gas leakage through the discharging apparatus.

In accordance with the present invention we provide a process of producing gas by heating coal or another gas-producing material within a gasifier under pressure, whereby gas and also ash particles are produced, the ash particles being discharged from the gasifier by:10 confining a liquid within a first path having a volume of the liquid with a free surface in communication with the gas pressure at the ash particle discharge end of the gasifier; discharging the ash particles into the said volume of the liquid through the free surface thereof; maintaining a continuous flow of the liquid along a second path, at a pressure lower than the pressure of the liquid in the first path; and continuously removing successive incremental volumes of liquid together with ash particles entrained in the liquid from the first path, and adding the said successive incremental volumes of the liquid together with entrained ash particles to the liquid flowing in the second flow path.

Preferably the successive incremental volumes of ash particles and liquid are removed from the first path by maintaining a continuous flow of liquid and entrained ash particles from the volume in communication with the pressure conditions within the gasifier into an incremental volume removal position within the first path. At this position, the flow of ash particles above a predetermined size are blocked while the flow of water and ash particles less than the aforesaid predetermined size are allowed to flow beyond the incremental volume removal position. These blocked particles and the liquid entraining the same constitute the successive incremental volume removed. It is also preferable - 3 41619 that for each successive incremental volume of liquid and entrained particles removed from the first path and communicated with the second path a corresponding incremental volume of liquid is removed from the second path and communicated with the water in the first path, so that an equal volumetric exchange between the paths takes place, resulting in a net flow of particles from the first path to the second path and an equal net flow of liquid from the second path to the first path. Preferably, this equal volumetric exchange is performed so that it is substantially constant at all times.

Furthermore, we provide apparatus for producing gas from coal or another gas-producing material, comprising a gasifier provided with means for receiving gas-producing material and continuously heating it under pressure, whereby gas and also ash particles are produced, and means for continuously removing ash particles, wherein the ash removal means comprise: (a) means for confining a liquid within a first path whereby there is a volume of the liquid which has a free surface in communication with the pressure within the gasifier, whereby ash particles produced within the gasifier are received within the said volume by passage through the said free surface; (b) means for maintaining a continuous flow of the liquid along a second path, at a pressure lower than the pressure of the liquid in the first path; and (c) means for continuously removing from the first path successive incremental volumes of liquid together with the ash entrained in the liquid, and adding the said successive incremental volumes of ash and entrained liquid to the liquid flowing in the second path.

In terms of apparatus, the aforementioned volumetric exchange is performed by a known device (see, for example, Swedish Patents Nos. 174,094 and 324,949) which includes a driven pocketed wheel and a particle blocking screen. In the volumetric exchange leakage is allowed to occur from the high pressure first path to the low pressure second path so that it is not essential to maintain an absolute seal during operation. - 4 41619 The leakage and amount of water and fine particles which are allowed to flow beyond the incremental volume removal position in the first path is coordinated with liquid input into the volume within the first path sufficient to maintain the free surface within a desired level range and the temperature of the liquid at a desired temperature below boiling. Desirably, the amount of flow beyond the incremental volume removal position is sufficient to cause the ash particles which have previously entered the volume of water in communication with the gasifier pressure to be directed by the velocity of flow into the open wheel pocket or pockets. However, the flow beyond the screen which consists of water and fine ash particles, must be handled downstream of the incremental volume removal position. Due to the fine particles in the water and the high pressure of the mixture, wear on the confining strucutre can become a problem, particularly confining structure having moving parts, such as valves and pumps. Where the amount of flow is regulated by a level responsive throttling valve, the wear characteristics are such as to require the utilization of costly antiabrasive materials in the throttling valve structure. Another disadvantage of the use of a level responsive throttling valve is that it reduces the high pressure of the flow to atmospheric pressure without efficiently utilizing the pressure loss occasioned thereby. Consequently, in order to prevent this pressure loss, the flow beyond the incremental volume removal position can be recirculated to the volume in communication with the gasifier pressure, in which case, only the pump used to recirculate would be subject to wear. Fines removal without appreciable pressure drop can be utilized to control wear, if necessary.

The present invention also provides, in another embodiment, incremental volume removal without the utilization of controlled particle directing flow through the sluicing device. Since the particle removal function takes place in a high pressure medium, the high pressure water leakage alone (or in conjunction with a mechanical assist such as movable baffles or the like) can be utilized - 5 1 to direct the gravity movement of the particles into the open pocket or pockets in which case, the known device is modified simply by replacing the screen with solid metal or equivalently blocking the screen slots.

The invention may best be understood with reference to the accompanying drawings wherein illustrative embodiments are shown.

In the drawings: Figure 1 is a schematic flow diagram illustrating one embodiment of the procedural steps of the present method and an apparatus of the present invention for carrying out the procedural steps of the method; Figure 2 is a perspective view of a transfer device used in the apparatus of the invention; Figure 3 is an exploded perspective view illustrating certain parts of the transfer device shown in Figure 2; Figure 4 is a schematic flow diagram illustrating another embodiment of the procedural steps of the present method and an apparatus of the present invention for carrying out the procedural steps of the method; and Figure 5 is a schematic flow diagram illustrating a further embodiment of the procedural steps of the present method and an apparatus of the present invention for carrying out the procedural steps of the method.

Referring now more particularly to the drawings, there is shown in Figure 1 thereof a schematic flow diagram illustrating the procedural steps of the present method. These steps include maintaining a volume of liquid, generally indicated at 10, having a free surface 12 in pressure communicating relation with the discharge end of a coal gasifier vessel, indicated at 14 in the drawings. It will be understood that while the drawings illustrate the volume of liquid 10 to be contained within the bottom end of the gasifier vessel 14, a separate vessel may be provided which is in pressure (e.g. 300 psi and above) communication with the discharge end of the gasifier 14 and which is capable of receiving the ash particles discharged from the discharge end of the - 6 41619 gasifier. With the arrangement shown, the ash particles which break up and fall into the discharge end of the gasifier vessel 14 by rotation of the fixed coal bed grate (not shown) fall into the liquid volume 10 penetrating the upper free surface 12 thereof.. While the present invention is particularly suited to fixed bed gasifiers, the invention may advantageously be utilized with any known gasifier where internal pressure conditions must be maintained. It is preferred; in accordance with the present invention to utilize water as the liquid. The ash particles are normally quite hot, above the flash point of water. Some flashing of the water occurs as the ash enters the water but this flashing will not be detrimental to the gasification process within the vessel 14 since steam is usually used as a reactant gas during the gasification. The free water surface 12 provides a seal to prevent gases under pressure within the gasifier vessel 14 from escaping and such water level is maintained nearly constant, as hereinafter more particularly explained.

The present method includes the establishment of a flow of water from the volume 10 along a first flow path, generally indicated at 16, which is maintained by the pressure within the gasifier vessel 14 acting on the free surface 12. The water flowing from the volume 10 along the first flow path 16 includes ash particles entrained therein and at a transfer position downstream from the volume 10, successive volumes of ash particles entrained in water are substantially continuously removed from communication with the first flow path while water with ash particles of a predetermined small size are permitted to flow downstream along the first flow path.

The present method includes the establishment of a flow of water along a second flow path 18 at a pressure less than that of the water in the first flow path 16. As shown, flow along the second path 18 is maintained by a pump 20 which draws water from a conduit 22 and discharges the same into a conduit 24. At a transfer position in the second flow path, downstream of the pumping position, the successive volumes of ash particles entrained in water - 7 41619 removed from the first flow path 16 are substantially continuously communicated with the water in the second flow path.

The procedure of continuously transferring communication of successive volumes, of water entrained ash particles from the first high pressure flow path to the second low pressure flow path is accomplished by a transfer or sluicing device, generally indicated at 26, which is communicated with the first flow path by a conduit 28, and with the second flow path by the conduit 24.

The method of the present invention includes the step of substantially continuously separating the ash particles from the water in the second flow path at a separation position downstream of the transfer position. While any suitable known device may be used to effect this separation, a preferred device shown in the drawings is in the form of an endless foraminous conveyor belt arranged to be continuously moved in a position above a water collecting tank or receptacle 32. With this arrangement water and ash particles flowing in the second flow path from the transfer device 26 is simply directed onto the upper flight of the foraminous belt 30 by a conduit 34. It will be understood that the size of the openings in the foraminous belt 30 are such that the ash particles are retained on the upper surface of the upper flight and carried thereby to a spaced discharge position. Water discharging from the conduit 34 onto the foraminous belt passes through the openings therein and is collected in the receptacle 32.

An advantage of utilizing a foraminous belt is that is may also be utilized along with the receptacle 32 to effect a separation between the small ash particles and water flow-in the first flow path 16 downstream of the transfer position thereof. As shown, this dual performance can be achieved by means of a conduit 36 extending from the transfer device 26 which discharges above the upper flight of the belt 30. The ash particle-water separation is performed, as before, with the ash particles being carried to the discharge position and - 8 41619 discharged with the larger particles separated from the liquid of the second flow path. It will be understood that the foraminous belt 30 can be maintained in an unclogged condition by the usual practice of back washing the return flight.

The utilization of a common receptacle 32 for the separated water in both flow paths is desirable from the standpoint of heat exchange and minimizing the pumping and controls. With the arrangement shown, the water held in receptacle 32 is used for the second flow path by simply connecting supply conduit 22 with the interior of the receptacle. The water in receptacle 32 is also used to maintain the level of surface 12 of water volume 10 in the bottom of vessel 14. This is accomplished by pumping water therefrom by a pump 38 communicated therewith by a supply conduit 40, to the volume 10 by a conduit 42.

Since the ash particles enter the water of the first high pressure flow path at temperatures above the boiling point of water and successive volumes of ash particles and water from the first high pressure flow path are continuously transferred to the second low pressure flow path, the water temperature in both flow paths will eventually reach the boiling point unless steps are taken to control this temperature increase. Such control is provided in accordance with the present invention by utilizing fresh cool water as part of the water source for maintaining the volume 10, along with the water from tank 32 pumped therein through conduit 42 by pump 38. As shown, fresh cool water is supplied to the volume 10 through a conduit 44 connected between the vessel 14 and the pressure side of a pump 46, and the suction side is communicated with a fresh cool water supply by conduit 48. The amount of cool water utilized is just sufficient to maintain the water temperature in the system from increasing beyond a predetermined temperature. This temperature is preferably sensed in the volume 10 by conventional temperature sensing means 50 which is utilized to regulate a flow control valve 52 in conduit 44, also in accordance with conventional practice. The level of the surface 12 of water - 9 41619 volume 10 is maintained by conventional level sensing means 54 which is utilized to regulate a throttling valve 56 in conduit 36.

The level of water volume 10 tends to increase because of water being supplied by pumps 38 and 46. The level tends to decrease because of leakage within the transfer device 26. The net tendency for change in level is to increase the level since the rate of flow from pumps 38 and 46 is greater than the leakage. The level is maintained constant by the throttling valve 56 set to control the level. This level control also provides for continuous flow through the transfer device 26 in the first flow path. The introduction of new water from the temperature control system results in a net gain of water in tank 32. This net gain is drained through level control valve 58. The draining of water from tank 32 and the addition of new water tends to reduce the concentration of very small fines thus allowing pumps 20 and 38 to operate on minimal abrasive materials.

It can be seen that the transfer device 26 is a significant component in the combination forming the apparatus of the present invention. The preferred device 26 is known per se for use with pulp digesters and is disclosed in the aforesaid Swedish Patents Nos. 174,094 and 324,949. As best shown in Figures 2 and 3, the device 26 includes a housing 60 having an open upper end 62 communicating with conduit 28 of the first flow path and a lower open end 64 (see Fig. 1) which communicates with conduit 36. The housing 60 of the transfer device 26 also includes an inlet 66 which receives low pressure water flowing in the second flow path 18 coming from the pump 20 through conduit 24, and an outlet 68 which discharges into conduit 34. Transfer device 26 is shown in solid lines in Figure 1 in communicating relation with the first flow path 16, the communication with the second flow path 18 being shown in dotted lines.

As best shown in Figures 2 and 3, the transfer device 26 includes a wheel 72 formed with four independent through going pockets 74, arranged as two crossing pairs, each pair being radially offset from the other by 45° thus - 10 41619 presenting four open ports equally spaced around the periphery of the wheel for each pair of pockets. The pocketed wheel 72 is encased by housing 60 and mounted for rotation within a housing liner 76. As best shown in Figure 2, the liner 76 includes four ports, 78, 80, 82 and 84, equally spaced around the periphery of the housing which register respectively with inlet 62, inlet 66, outlet 64 and outlet 68. Each port has a width which is greater than the sum of the widths of two pockets 74 in the pocketed wheel and a divider 86 is located midway in each housing port to separate the same into two parallel ports, as clearly depicted in Figures 2 and 3.

The pocketed wheel 72 may be either cylindrical or tapered; illustration of such being shown in Figures 2 and 3 as tapered with wheel diameter increasing in the direction of a clearance adjusting hand wheel 88. Tapering of the wheel 72 provides for adjustment of the clearance between the wheel 72 and housing liner 76; additionally, increase in clearance due to wear can be taken up by turning hand wheel 88 pushing wheel 72 toward a shaft drive end 90 shown in Figure 2. The pockets 74 through wheel 72 of each pair slide in and out of register with pockets in the other pair so as to provide continuous passage through the wheel. While sliding in and out of register, the overall cross sectional area available for through flow of water and ash particles remains substantially constant.

Ash particles entering the transfer device 26 with water through inlet 62, under the gas pressure of the gasifier, are moved through ports 78 and 82. A screen 92 is disposed within each port 82 so that fine ash particles of the predetermined size range larger than the screen opening are thus held in the communicating wheel pocket 74. As the filled pocket 74 rotates and begins to approach a position nearly perpendicular to its filling position, low pressure water in the second flow path 18 from pump 20 is forced through conduit 24 and port 80 into the pocket causing discharging of ash particles from the pocket through port 84 into conduit 34. Before the pocket again rotates to the filling position all ash particles are emptied into conduit 34 leaving only water in the - 11 41619 pocket. The pocketed wheel 72 rotation is continuous but the filling and emptying of pockets in a single pair of pockets is intermittent. Since the adjacent parallel pair of pockets, displaced 45 degrees peripherally, is also intermittently filling and discharging, the sum of these two intermittent filling and discharging pairs of pockets is continuous. The continuous operation is an effect of the peripheral displacement of the two parallel pairs of pockets, such displacement being shown in Figure 3, for as a pocket is closing to housing inlet port a pocket is opening to the same port, thus always maintaining a constant open cross section through the first flow path via ports 78 and 82 and the second flow path via ports 80 and 84 making the two flow paths continuous.

The transfer device 26 is uniquely characterized by several important internal features. The first of these is the ability to transfer ash particles from one flow path to another flow path at lower pressure without the need for positive sealing surfaces. In accordance with the present invention the rotating pocketed wheel 72 need not come into intimate contact with the housing liner 76 but May present a clearance therewith. Since ports 78 and 82 are at a higher pressure than ports 80 and 84 a leakage occurs in the form of water flow from ports 78 and 82 to ports 80 and 84 through the clearance. The water flow through the clearance is maintained small by maintaining the clearance narrow.

The small water flow provides a lubrication and cleaning function which prevents binding of rotating wheel 72 with housing liner 76. Secondly, another unique feature of the transfer device 26, is the screening out of fine material through screens 92. During filling of a pocket 74 in the rotating wheel 72, fine ash particles are drawn through the peripheral slots in screens 92. The slots remove particles below a predetermined small size (e.g, approximately 3 m). The constructional form of the transfer device 26 is such that self-cleaning of the screens 92 is provided, such cleaning being performed by the edge of the rotary wheel pocket as the edge passes over the slots. Thirdly, the liner 76 may be - 12 41619 provided with one or more grooves 94 adjacent the port openings 78 and 82, as shown in Figure 3. The grooves 94 are formed with a peripheral dimension which is greater than the dimension measured in the radial direction, so that ι a liquid flow at high pressure into the pocket openings 78 and 82 is exposed to 5 strong choking action. Consequently, shocks and vibrations originating on pocket to port opening are milder reducing the tendency of ash particles to break. Lastly, the water used as a conveying medium tends to prevent cutting of ash particles when the rotating wheel pocket edge closes housing filling port 80 to the wheel pocket with the wheel 72 rotating at a low RPM, preferably 1 to 10 RPM. The water provides some buoyancy to the ash particles and the pocket edge will tend to push the particle away rather than pinch or cut off the particle between the pocket edge and the housing filling port edge. As the pocket being filled closes off to the filling port, the pocket in the parallel pair of pockets is approaching full open to the filling port so that the majority of water flow is through this pocket, carrying all of the particles into this pocket, leaving none or nearly none to be pinched off by the closing pocket.

The flow of high pressure water which is maintained through the screens 92 tends to direct the ash particles to move into the pocket or pockets which are open and hence to prevent deposit of ash particles on the periphery of the wheel which is blocking the inlet of the ash particles into the pockets.

This action tends to reduce wear on the wheel periphery. However, the directing flow through the wheel pockets results in the necessity to handle a flow of high pressure water and entrained fine ash particles downstream of the screens 92. In the arrangement described above for handling this flow, abrasive resistant materials must be utilized in the construction of the throttling valve 56 in order to prevent too frequent shut down for replacement of worn valve parts. The wear characteristics of a valve operable to throttle a high pressure flow of water and fine ash particles to atmospheric pressure are exceedingly demanding. - 13 41619 Moreover, while this throttling action enables the system to utilize a simple single separator 30 operating at atmospheric pressure for both the large and fine ash particles, it also involves substantial pressure losses.

In Figure 4 there is shown a schematic diagram of a system embodying the principles of the present invention illustrating modifications in Which the energy losses attendant to throttling of the high pressure flow to the atmosphere are minimized. The system of Figure 4 also illustrates procedures for insuring against blockage of the sluicing device by the pressure of oversize ash particles lodging in the inlet.

Referring now more particularly to Figure 4, the apparatus shown therein includes a gasifier vessel 110, the discharge end of which communicates with an annular housing assembly 112, The housing assembly includes an upper section 114 which communicates with the interior gas pressure of the gasifier vessel 110 and is configured to receive therein suitable ash particle breaking means 116. While the breaking means 116 may be of a conventional type, such as, single roll, swing hammer or jaw type, a preferred double roll type is schematically illustrated in Figure 4. It is important to note that the double roll breaking means 116 is contained within the housing section 114 so that the rolls operate under the gasification vessel pressure conditions which normally exceed 300 psig.

It will be noted that as the ash particles drop by gravity from the gasifier vessel 110, they will pass between the dual breaker roll of the breaking means 116. The spacing of the rolls is co-ordinated with the size of the sluicing device utilized exemplary setting being between 4 to 6 inches. Ash particles of a size less than the roll spacing (e.g, 4 inches) will pass from the gasifier vessel 110 through the upper housing section 114 into a lower housing section 118. The lower housing section 118 which is in the form of an annular wall serves as a part of the means for confining liquid such as water within a first path. The liquid in the first path includes a volume within the housing section 118 having a free surface 120 which communicates with the gas - 14 41619 pressure conditions within the gasifier vessel 110.

The smaller ash particles thus pass directly into the volume of water within the housing section 118 downwardly through the free surface 120. Ash particles larger than the spacing between the breaker rolls will be engaged thereby and broken up before passing downwardly through the free water surface 120. Although the breaker rolls 116 are shown above the free surface 120 for dry operation, they could be located below the free surface for wet breaking, if desired.

The lower end of the housing section 118 opens to the upper inlet of a sluicing device 122 which is constructed like the sluicing device 26 previously described.

In the embodiment shown in Figure 4, means for confining the high pressure water within the first path includes a suitable conduit 124 leading from the lower outlet of the sluicing device 122 to the section side of a centrifugal pump 126, a conduit 128 leading from the pressure side of the pump to an inline drainer 130 and a conduit 132 leading from the inline drainer back into the interior of the housing section 118.

With this construction the first path is circulatory from the housing section 118, through the sluicing device 122 and back to the housing section 118 so that the high pressure of the liquid is not dissipated to atmosphere as is the case with the use of the throttling valve 56. Pump 126 requires very little energy to operate since it primarily performs a circulating function, its pressurization function being limited to that required to overcome line losses.

Pump 126 is subjected to wear since it is operating on water having fine ash particle entrained therein. However, it will be noted that the wear is considerably less than that imposed upon throttling valve 56 since high velocity flows of the intensity of those created in the latter are not imposed on the moving parts of the pump 126. The pressure (e.g. 5 to 10 feet of HgO) and wear requirements of pump 126 are well within existing slurry pump capabilities.

Inline drainer 130 is provided as a simple but effective device and - 15 41619 procedure for providing a source of ash particle free water within the first flow path which can be drained off to maintain the free surface 120 within a desired constant level range and the water defining the same within a desired temperature below boiling. The inline drainer constitutes a generally cylindrical housing having a cylindrical screen mounted concentrically therein inline with the flow. The velocity of flow through the drainer is such that the major quantity of liquid and almost all the small ash particles in the flow are directed longitudinally through the drainer within the screen such that the screen does not tend to clog. A minor quantity of liquid can be drained from the interior periphery of the housing without inducing appreciable movement of the fine ash particles into·-or through the openings of the screen.

The means for maintaining a flow of water at a reduced pressure along a second flow path is illustrated schematically as a supply conduit 134 leading from a water supply to the suction side of a centrifugal pump 136, a'conduit 138 leading from the pressure side of the pump 136 to the side inlet of the sluicing device 122 and a conduit 140 leading from the side outlet of the sluicing device 122.

Conduit 140 leading from the sluicing device 122 directs the ash particles and water to an independent ash and water separation facility which is not schematically illustrated in the drawings. The independent facility may be a settling pond, thickener or any mechanical facility which recovers ash for product use. The water supply for supply conduit 134 is likewise not shown but may be a fresh water source or the purified water from the independent ash particle separation facility.

Level and temperature control of the water within the housing .ection 118 is maintained by draining liquid from the-circulatory first path through the drainer 130 into the second path when the temperature of the water volume reaches a predetermined value below boiling sufficient to prevent flashing within the sluicing device due to pressure drop. As shown this drainage is accomplished by sensing the temperature of the water, by a temperature sensing - 16 41619 mechanism 142 within the water which operates a drain valve 144 within a conduit 146 leading from the drainer 130 to the inlet conduit 138 of the second path.

The water temperature is lowered by the introduction of a supply of cool water into the housing section 118 through a conduit 147 leading from the supply (not shown) to a sensing mechanism 150 and a conduit 152 leading from the valve 148 to the interior of the housing section 118.

Under most operating pressures, the leakage within the sluicing device 122 from the high pressure first path to the low pressure second path would be greater than the net flow of water from the second flow path to the first flow path due to ash particle displacement. Consequently, it would be expected that temperature controlled valve 144 would remain closed most of the time while cool water supply valve would be open most of the time to maintain the water level and hence the desired temperature level. Where lower operation pressures are expected and as an added safety feature under any conditions to prevent the flooding of water upwardly into the gasifier vessel discharge end, a high level sensing mechanism 154 is mounted within the housing section 118 for controlling a safety valve 156 mounted within a conduit 158 leading from the drainer 130 to the second path inlet conduit 138.

The apparatus of Figure 4 has the advantage of avoiding the pressure loss occasioned by throttling to atmospheric pressure as with the system of Figure 1. This advantage is achieved by recirculation and therefore the system has a greater tendency for fines to become concentrated in the water within the first path. It should be noted however that since the fines passing through the sluicing device screen are recentered into the water above the sluicing device many of these fines will again pass through a pocket of the sluicing device 122 which is partially filled and will therefore be retained with these particles by a straining action for passage into the second path after filling. Sufficient fines are sluiced away in this fashion to prevent fines build up to the point of requiring shut down and removal. Should fines concentration become significant, a cyclone could be used in lieu of the inline drainer 130 to separate out the - 17 41619 fines. The pressure drop loss can be minimized by restricting the underflow outlet or by providing dual outlet valves. The disadvantages of the cyclone pressure loss may be offset by savings in pump wear by placing the cyclone upstream of the pump so that its overflow outlet communicates with the suction side of the pump. Similarly a cyclone could be utilized to reduce wear on the throttling valve 56.

Figure 5 illustrates an embodiment of the present invention in which means for confining the water within the first path are simplified by eliminating flow through the lower sluicing device outlet. This apparatus and process simplification is somewhat offset by the lack of positive circulation of the ash particles into the sluicing device pockets. In Figure 5, a gasifier vessel 210 is shown with its discharge end in communication with housing 212 which confines the water within the first path, including the volume having free surface 214 downwardly through which the ash particles from the vessel Pass. It will be understood that suitable ash particle breaking means similar to that shown in Figure 4 may be provided if desired as is also the case with the apparatus of Figure 1. Likewise the apparatus of Figure 4 may be utilized without the ash particle breaking means 116 shown therein.

Housing 212 leads to the upper inlet of a sluicing device 216 which is constructed like the device 26 previously described except that screens 92 are replaced by solid plates. The second, low pressure flow path is provided by supply conduit 218, pump 220, inlet conduit 222 and outlet conduit 224 in a manner similar to that provided in the apparatus of Figure 4. Level and temperature control of the water in housing 212 is maintained by temperature sensing means 244 controlling valve 226 connected to conduits 228 and 230 and level sensing means 232 controlling valve 234 connected to cool water supply conduit 236 and conduit 238 leading into the housing 212. Conduit 228 leads from the interior of the housing 212 to the temperature control valve 226 while conduit 230 leads from the valve to the inlet conduit 222 of the second path. - 18 41619 In order to protect the valve from fine ash particles as much as possible, a screen 240 is provided within the housing in surrounding relation to the inlet to conduit 228. An anticlogging device, such as a moving wiper (not shown), may be utilized with screen 240, if desired. A safety valve 246, similar to valve 156, operated by a high level sensing mechanism 248 may be mounted in parallel with temperature sensitive valve 226.

In this embodiment, leakage through the sluicing device 216 will more than offset the ash particle displacement from the second flow path, such leakage providing some flow directing tendency of the ash particles within the water volume toward the sluicing device pockets. Gravity flow of the particles within the water is also relied upon to fill the pockets. This embodiment is particularly suited to very slow wheel speeds of 1 RPM and below. A sluicing device of greater capacity than that needed in the other embodiments may be desirably used.

Claims (42)

1. A process of producing gas by heating coal or another gas-producing material within a gasifier under pressure, whereby gas and also ash particles are produced, the ash particles being discharged from the gasifier by: confining a liquid within a first path having a volume of the liquid with a free surface in communication with the gas pressure at the ash particle discharge end of the gasifier; discharging the ash particles into the said volume of the liquid through the free surface thereof; maintaining a continuous flow of the liquid along a second path, at a pressure lower than the pressure of the liquid in the first path; and continuously removing successive incremental volumes of liquid together with ash particles entrained in the liquid from the first path, and adding the said successive incremental volumes of the liquid together with entrained ash particles to the liquid flowing in the second flow path. - 19 41619

2. A process as defined in Claim 1 wherein the successive incremental volumes are removed from the first path by maintaining a continuous flow of liquid together with entrained ash particles from the said volume into an incremental volume removal position within the first path; blocking the flow of ash particles above a predetermined size at the said incremental volume removal position while permitting the liquid together with entrained ash particles less than the said predetermined size to flow beyond the said incremental volume removal position; and removing successive volumes of blocked particles, entrained in liquid at the time of their removal, so as to provide the said incremental volumes.

3. A process as defined in Claim 2 wherein the continuous flow of the liquid together with entrained ash particles from the said volume in the * first path is maintained by pumping a portion of the liquid flowing beyond the said incremental volume removal position back into the said volume without reducing the pressure thereof to that for atmospheric conditions.

4. A process as defined in Claim 2 or 3, including the step of separating ash particles from the liquid flowing along the second flow path.

5. A process as defined in Claim 4 including the step of separating ash particles less than the said predetermined size from the liquid in the first flow path at a separation position downstream from the said incremental volume removal position.

6. A process as defined in Claim 5 wherein the separation of the ash particles from the liquid, in both paths, is accomplished by directing the liquid together with entrained ash particles in both paths on to a continuously moving endless foraminous conveyor belt, the ash particles being retained on the belt and subsequently discharged therefrom at a spaced discharge position, while the liquid passes therethrough.

7. A process as defined in Claim 6 wherein the liquid which in both paths is separated from the ash particles by passage through the said belt is collected in a common receptacle. - 20 41619

8. A process as defined in Claim 7 wherein the first path is maintained by pumping the liquid from the common receptacle to the said volume.

9. A process as defined in Claim 8 wherein the said volume is maintained at a predetermined temperature below boiling, and at a predetermined level, by sensing the temperature thereof and introducing cool liquid therein according to the liquid temperature sensed, and by sensing the liquid level in the said volume and throttling the flow along the first path at a throttling position between the said incremental volume removal and separation position according to the level sensed.

10. A process as defined in Claim 3 or 4 wherein the volume of liquid within the first path is continuously maintained below its boiling temperature, and the free surface thereof is continuously maintained within a predetermined range of levels, by continuously sensing the temperature of the volume of the liquid in the first path, directing liquid having an excessively high temperature from the first path into the second path when the temperature sensed is above a predetermined value, sensing the level of the said free surface, directing liquid from the said volume into the second path when the level sensed is above a predetermined value, and directing a supply of low temperature liquid into the said volume when the level sensed is below a predetermined value.

11. A process as defined in any of Claims 1 to 10, wherein, for each successive incremental volume of liquid together with entrained particles removed from the first path and added to the liquid flowing in the second path, a corresponding incremental volume of the liquid is removed from the second path and added to the liquid in the first path, whereby an equal volumetric exchange between the two paths, takes place and there is a net flow of particles from the first path to the second path and a corresponding net flow of the liquid from the second path to the first path.

12. A process as defined in Claim 11 wherein the equal volumetric exchange between the two paths is performed continuously and the quantity of the liquid exchanged between the two paths is constant. - 21 41619

13. A process as defined in any of Claims 2 to 10, or in Claim 11 or 12 when read with Claim 2, including the step of reducing the ash particles to a size below a predetermined value while they are between the ash particle discharge position and the incremental volume removal position.

14. A process as defined in Claim 13 wherein the ash particle size reduction is performed before the ash particles are discharged through the free surface of the said volume of the liquid in the first path.

15. A process as defined in Claim 13 or 14 wherein the ash particle size reduction is accomplished by passing the ash particles between a cooperating pair of rolls.

16. A process as defined in Claim 1 wherein the successive incremental volumes are removed from the first path by directing the liquid together with the ash particles entrained in the liquid into an incremental volume position within the first path; blocking the movement of the ash particles at the incremental volume removal position; and removing successive volumes of blocked particles, entrained in the liquid at the time of their removal, so as to provide the said incremental volumes.

17. A process as defined in Claim 16 wherein the volume of the liquid within the first path is continuously maintained below its boiling temperature, and the free surface thereof is continuously maintained within a predetermined range of levels, by continuously sensing the temperature of the volume of the liquid in the first path, directing liquid having an excessively high temperature from the first path into the second path when the temperature sensed is above a 4 predetermined value, sensing the level of the said free surface, directing liquid from the said volume into the second path when the level sensed is above a predetermined value, and directing a supply of the liquid at a low temperature into the said volume when the level sensed is below a predetermined value.

18. Apparatus for producing gas from coal or another gas-producing material, comprising a gasifier provided with means for receiving gas-producing material and continuously heating it under pressure, whereby gas and also ash - 22 41610 particles are produced, and means for continuously removing the ash particles, wherein the ash removal means comprise: (a) means for confining a liquid within a first path whereby there is a volume of the liquid which has a free surface in communication with the pressure within the gasifier, whereby ash particles produced within the gasifier are received within the said volume by passage through the said free surface; (b) means for maintaining a continuous flow of liquid along a second path, at a pressure lower than the pressure of the liquid in the first path; and (c) means for continuously removing from the first path successive incremental volumes of liquid together with the ash entrained in the liquid, and adding the said successive incremental volumes of ash and entrained liquid to the liquid flowing in the second path.

19. Apparatus as defined in Claim 18 wherein the means (c) comprises a sluicing device comprising a housing having a first path inlet and outlet and a second path inlet and outlet provided therein, a wheel rotatably mounted in the housing having a plurality of through-going pockets extending therethrough for alternately communicating between the first path inlet and outlet and between the second path inlet and outlet upon rotation thereof within the housing, and a screen provided in the first path outlet.

20. Apparatus as defined in Claim 19 wherein the first path inlet includes a pair of first inlet ports spaced axially with respect to the rotational axis of the said wheel, the first path outlet including a pair of axially spaced first outlet ports axially aligned with and displaced 180° from the first inlet ports with respect to the said rotational axis, the second path inlet including a pair of axially spaced second inlet ports axially aligned with and displaced 90° from the first inlet ports, the second path outlet including a pair of axially spaced second outlet ports axially aligned with and displaced 180° from the second inlet Ports; the said wheel including two axially spaced pairs of through-going independent pockets arranged as two crossing pairs, each pair being offset radially from the other by 45°; the openings of the ends of the said pockets - 23 41619 being so related to the cross-sections of the said ports that each pocket end, during the rotation of the said wheel, moves progressively from a position of substantially zero communication to full communication, and then back to substantially zero communication, with each successive port axially aligned therewith.

21. Apparatus as defined in Claim 19 or 20 wherein the said wheel is tapered, the said housing is correspondingly tapered, and an adjusting means is provided for setting the clearance between the said tapered wheel and the said tapered housing.

22. Apparatus as defined in Claim 19, 20 or 21 wherein the said housing includes a liner within which the said wheel is mounted.

23. Apparatus as defined in Claim 22 wherein the liner is formed with grooves adjacent the edges thereof defining the first inlet and outlet ports, the grooves having a peripheral dimension which is greater than the dimension ( measured in the radial direction.

24. Apparatus as defined in any one of Claims 19 to 23 wherein the means (a) 1 ' includes'an annular wall for confining the said volume, communicating means connecting the lower end of the annular wall with the first path inlet, a first conduit connecting the first path outlet with the interior of the annular wall, and a first pump in the first conduit.

25. Apparatus as defined in Claim 24 wherein the means “(b) comprises a second conduit leading into the second path inlet, a second pump in the second conduit, and a third conduit leading from the second path outlet.

26. Apparatus as defined in Claim 25 including: an inline drainer in the first conduit, downstream of the first pump; a fourth conduit leading from the inline drainer to the second conduit, at a position downstream of the second pump; a first level-responsive valve in the fourth conduit; a first levelsensing means within the annular wall, for sensing the level of the free surface of the volume of the liquid contained therein and operating the first levelresponsive valve; a cold liquid supply conduit leading to the interior of the - 24 41619 annular wall; a second level-responsive valve within the cold liquid supply conduit; a second level-sensing means within the annular wall, for sensing the level of the free surface of the volume of the liquid contained therein and operating the second level-responsive valve; a temperatureresponsive valve within the fourth conduit in parallel with the first levelresponsive valve; and a temperature-sensing means within the annular wall for sensing the temperature of the volume of the liquid contained therein and for operating the temperature-responsive valve.

27. Apparatus as defined in any one of Claims 19 to 23 wherein the means (a) includes a conduit leading from the first path outlet; a throttle valve in the said conduit; a level-sensing means for sensing the level of the free surface of the said volume of the liquid and operating the throttle valve to control the level of the said free surface; a temperature-sensing means for sensing the temperature of the said volume of the liquid; and means operable in response to the temperature-sensing means for introducing a supply of cool liquid into the said volume to maintain the temperature thereof at a predetermined temperature below boiling.

28. Apparatus as defined in Claim 27 including means for separating fine ash particles and liquid flowing in the said first path downstream of the throttle valve.

29. Apparatus as defined in Claim 28 wherein the said separating means comprises a continuously movable endless foraminous conveyor belt disposed so as to receive the fine ash particles and liquid flowing downstream of the throttle valve, whereby ash particles are retained thereon and subsequently discharged therefrom at a discharge position spaced away from the receiving position, while the liquid passes therethrough, a receptacle being provided for receiving the liquid passing through the said belt.

30. Apparatus as defined in Claim 29 wherein the means (b) includes means for directing the liquid and ash particles in the second flow path flowing downstream of the second path outlet on to the said belt, whereby ash particles - 25 41619 are retained thereon and subsequently discharged at the said discharge position, while the water passes through the said belt into the said receptacle.

31. Apparatus as defined in Claim 30 wherein the means (b) includes a conduit leading from the said receptacle to the second path inlet, having a pump therein.

32. Apparatus as defined in Claim 29, 30 or 31 wherein the means (a) includes a pump for pumping the liquid from the said receptacle into the said volume of the liquid.

33. Apparatus as defined in any one of Claims 18 to 32 and level control means is provided for maintaining the volume of the liquid in the first path at a temperature below boiling and the level of the free surface thereof within a predetermined range of levels.

34. Apparatus as defined in Claim 18 wherein the means (c) comprises a sluicing device comprising a housing having a first path inlet and a second , path inlet and outlet provided therein, a wheel rotatably mounted in the housing having a plurality of separate pockets extending therethrough for alternately communicating with the first path inlet and between the second path inlet and outlet upon rotation thereof within the housing, the sluicing device allowing some leakage between the first path and the second path.

35. Apparatus as defined in Claim 34 wherein the first path inlet includes a pair of first inlet ports spaced axially with respect to the rotational axis of the said wheel, the second path inlet including a pair of axially spaced second inlet ports axially aligned with and displaced 90° from the first inlet ports, the second path outlet including a pair of axially spaced second outlet ports axially aligned with and displaced 180° from the second inlet ports; the said wheel including two axially spaced pairs of through-going independent pockets arranged as two crossing pairs, each pair being offset radially from the other by 45°; the openings of the ends of the said pockets being so related to the cross-sections of the said ports that each pocket end, during the rotation of the said wheel, moves progressively from a position of substantially zero communication to full communication, and then back to substantially zero communication, with - 26 41619 each successive port axially aligned therewith.

36. Apparatus as defined in Claim 34 or 35 wherein the said wheel is tapered, the said housing is correspondingly tapered, and an adjusting means is provided for settling the clearance between the said tapered wheel and the 5 said tapered housing.

37. Apparatus as defined in Claim 34, 35 or 36 wherein the said housing includes a liner within which the said wheel is mounted.

38. Apparatus as defined in any one of Claims 18 to 26 wherein the means (a) includes a housing and ash particle breaking means within the 10 housing.

39. Apparatus as defined in Claim 38 wherein the ash particle breaking means includes a pair of spaced rolls.

40. Apparatus as defined in Claim 39 wherein the rolls are mounted within the said housing assembly above the free surface of the said volume 15 of the liquid in the first path.

41. A process as defined in Claim 1, substantially as described with reference to Figs. 1 to 3, Fig. 4 or Fig. 5 of the accompanying drawings.

42. An apparatus as defined in Claim 18, substantially as described with reference to Figs. 1 to 3, Fig. 4 or Fig. 5 of the accompanying drawings.