BACKGROUND OF THE INVENTION

(1 ) Field of the Invention

This invention relates to a method of, and apparatus for transfer of solid particles from a point at a pressure to a point at a higher pressure.

(2) Prior Art

The most general method of transferring solid from a low pressure to a high pressure is the use of locked hoppers. Working in a cycle, a hopper at low pressure is charged with solid, it is then isolated and pressurized up to the required high pressure before discharging the solid by gravity to the receiving vessel at the higher pressure. After complete discharge the hopper is then depressurized for the start of the next cycle. Two hoppers are generally used, one being charged while the other is being discharged. Other known methods for affecting transfer of solid to a higher pressure include the use of mechanical solid pumps, and the use of slurry pumps after converting the solid into a slurry. In the former case considerable problems exist through erosion of seal while the option of adding a liquid to the solid to create a slurry is unacceptable in many practical situations. The concept of feeding solids from a low pressure by using a series of standpipes has been described recently by "Teo, C.S. and Leung, L.S., in "Standpipe Flow - The Current Status and Future Applications", J. of Pipelines 2, 187-197 (1982)". Solids in the feed bunker are fed through a series of fluidized beds, standpipes, mechanical slide valves and risers operating at increasing pressure until the final process operating pressure is reached.

This system is extremely unstable to operate and it relies on the mechanical slide valves with moving parts to control operation in each standpipe, and is bulky with a

fluidized bed as a feeder to each standpipe. SUMMARY OF THE PRESENT INVENTION It is an object of the present invention to provide a method where particulate solids can be transferred to a higher pressure continuously and steadily in a device with few or no moving parts.

It is a preferred object to provide a solid feeder which can be operated over a range of solid flowrates and over a range of pressure differentials (e.g. from zero flow to a design maximum flow).

Other preferred objects of the present invention will become apparent from the following description.

In one aspect the present invention resides in a method for transferring solid particles from a first point at a pressure to a second point at a higher pressure including the steps of:

(a) arranging at least one standpipe and riser pair;

(b) feeding gas at a pressure through an inlet into the lower standpipe and gas at a higher pressure through an inlet into the lower end of the riser;

(c) feeding the solid particles into the upper end of the standpipe;

(d) fluidizing the solid particles in the standpipe to enable the solid particles to flow down the standpipe;

(e) transferring the solid particles from the lower end of the standpipe to the lower end of the riser through a valve means interconnecting the standpipe and the riser; and (f) causing the solid particles to travel up the riser due to the flow of the gas up the riser. Preferably the solid is fed from the riser to the standpipe of a second standpipe and riser pair and the method steps are repeated. Preferably in step (d), the flow of solid particles down the standpipe is countercurrent to the flow of

fluidizing gas up the standpipe.

In a second aspect, the present invention resides in an apparatus for the transfer of solid particles from a first point at a pressure to a second point at a higher pressure including: at least one standpipe and riser pair; means to feed the solid particles into the upper end of the standpipe; a gas inlet at the lower end of the standpipe connected to a source of gas at a pressure to feed the gas into the standpipe to fluidize the solid particles in the standpipe and enable the solid particles to flow down the standpipe; valve means to transfer the solid particles from the lower end of the standpipe to the lower end of the riser; and a gas inlet at the lower end of the riser, connected to a source of gas at a higher pressure, the flow of the gas up the riser causing the solid particles to travel up the riser.

Preferably the valve means is a V-valve, L-valve, J-valve or other non-mechanical valve. However mech¬ anical valves such as slide valves may be used.

Preferably the first standpipe is supplied with the solid particles from a bulk hopper connected to the upper end of the standpipe by a riser. Preferably the pressures in the standpipes and risers are con¬ trolled by an automatic pressure controller.

The gas outlets at the upper ends of the stand- pipes and risers may be connected to the gas inlets of preceding (i.e. lower pressure) standpipes and risers, respectively to form a substantially closed system.

BRIEF DESCRIPTION OF THE DRAWINGS

To enable the invention to be fully understood, a preferred embodiment will now be described with

reference to the accompanying drawings, in which:

FIG. 1 is a schematic arrangement for feeding solid particles from a bulk supply hopper (e.g. at atmospheric pressure) to a reactor at a number of atmospheric pressures;

FIG. 2 is an enlarged sectional view of detail

2 on FIG. 1 ;

FIG. 3 is an enlarged sectional view of detail

3 on FIG. 1 ; and FIG. 4 is a sectional front view taken on line 4-4 on FIG. 3-

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the solid feeder device 10 consists of a number of adjacent standpipes 11, 12, 13 and risers 14, 15 and 16 connected by valve assemblies 17, 18 (see FIGS. 3 and 4) at their lower ends and transfer leads 19, 20, 21 (see FIG. 2) at their upper ends. The normal operation of the feeder device 10 will now be described. Solids in an open bulk supply hopper 22, at atmospheric pressure, are metered through a valve 23 and are transported by a pneumatic conveyor 24, with a gas inlet 25, to the lower end of the riser 14. Gas, at a higher pressure, is fed to the inlet 26 at the lower end of the riser 14 and transports the solid up the riser to the transfer head 19.

Referring to FIG. 2, the transfer head 19 has a closed tubular body 27 with an inclined bottom wall 28 and horizontal top wall 29 provided with a gas outlet 30. The solid and gas from the riser 14 enters a separation tube 31 which has a downwardly directed exhaust port 32. Inertia and gravity direct the solid towards the bottom wall 28 of the transfer head 19 and through a transfer pipe 33 to the upper end of adjacent standpipe 11. (The solid arrows indicate the solids flow).

The finer solids may remain entrained in the gas (the flow of which is indicated by the broken arrows) and so the gas enters a cyclone 34 which separates the solids and directs the latter through an outlet pipe 35 towards the lower wall 28 of the transfer head and thereby the transfer pipe 33 and standpipe 11.

The solid in the standpipe 11 is fluidized from the lower end by a metered stream of gas through inlet 36 (see also FIG. 3). The solid flow down the stand¬ pipe 11, due to the head of solid in the standpipe, is countercurrent to the flow of gas fluidizing the solid up the standpipe.

At the lower end of the standpipe 11 , the solid is transferred to the second riser 15 by a valve assembly 17 (see FIGS. 3 and 4). The valve assembly 17 has a V-valve 37 which has its inlet 38 connected to the standpipe 11 and its outlet 39 connected to a transfer tube 40. A V-valve is a non-mechanical valve as described by Liu, J.L., Li, X.G. and Kwauk, M.S. in "Pneumatically Controlled Multistage Fluidized Beds" in Grace, J.R. and Matsen, J.M. (ed.) "Fluidization" 485-492, Plenum Press, New York (1980). (It will be readily apparent to the skilled addressee that other types of non-mechanical valves e.g. L-valves, and

J-valves can also be used without departing from the present invention).

Gas, at a higher pressure, is fed into the inlet 41 at the lower end of the transfer tube 40 and the solid is entrained in the gas and flows up the riser 15 to be transferred to the next standpipe 12 via the transfer head 20 at the top of the riser 15.

In turn, the solid flows down the standpipe 12, up the riser 16 and down the standpipe 13- ^' At the lower end of the standpipe 13, the solid flows through

a V-valve 37 into a receiver 42 which is at or above the desired highest pressure and the solid in the receiver 42 is metered to the reactor 43 through an isolating valve 44. The pressure at the upper ends of the standpipes

11-13 are controlled by valves 45, in the gas outlets 46 of the standpipes which are controlled by automatic pressure controllers 47 in the gas outlet 30 of the preceding risers 14-16 respectively. The pressure in the receiver 42 is controlled by a valve 48 which may be provided with an automatic controller (not shown).

To provide a closed system, the gas outlets 46 and 30 of the standpipe 13 and riser 16 may be connected to the inlets 36 and 41 of the standpipe 12 and riser 15, respectively, which are at a lower pressure and a similar arrangement may be provided between standpipes 12 and 11 and risers 15 and 14.

The bulk density of solid in each standpipe 11-13 is controlled to a valve close to that at minimum fluid- ization to permit maximum pressure gain in the stand¬ pipes due to the head of solid in each standpipe. This is achieved by controlling the gas flow rate through the inlets 36 into each of the standpipes 11-13 and by the use of a number of differential pressure controllers 48 (see FIG. 1). The pressure difference between a short section of standpipe 13 is measured by the controller 49 and the magnitude of any pressure fluctuation is con¬ trolled automatically to an acceptable level by venting a small amount of gas through the control valve 50. The acceptable level of pressure fluctuation corresponds to that measured in a fluidized bed near minimum fluidiz- ation velocity. (It will be readily apparent to the skilled addressee that each of the standpipes will have one or mere differential pressure controllers 48). While FIG. 1 shows a system with three stand-

pipes, there is no limit to the number of stand¬ pipes to be used in the device. The total pressure gain (defined as the pressure in the receiver 42 minus the pressure in the feed hopper 22) is dependent on the height and the number of standpipes. The pressure gain in each standpipe is proportional to the height of the standpipe (i.e. the head of solid) and the solid density. The weight of the solid in each standpipe may generate a pressure gain at the lower end of the standpipe relative to the upper end of e.g. 0.75 atmospheres, which is partially offset by the pressure loss of e.g. 0.1 atmospheres due to the fluid- ization of the solids in the standpipe. Therefore the total pressure gain for the standpipe is e.g. 0.65 atmospheres. A small pressure loss may also be incurred as the solids are transported up the risers to the next standpipe. However, the overall increase in pressure for each standpipe and riser pair may be e.g. 0.5-1 atmospheres and so the required pressure gain between the receiver 42 (or reactor 43) and the hopper 22 is obtained by the provision of sufficient standpipe and riser pairs so that their additive pressure gains equal, or exceed, the required pressure gain. In some processes it may be desirable to preheat or pretreat _. the feed solid from the gas from the high pressure receiver 42 (or reactor 43) in a continuous manner. This can readily be achieved by using the high pressure reactor gas for feeding into the last standpipe 13 and riser 16 (i.e. through inlets 26 and 41) and for using the gas leaving the last standpipe/riser (i.e. from 46/30) for the inlet of the preceding riser and standpipe (as hereinbefore described) and so on.

The valve assembly 17 in FIGS. 3 and 4 embodies the use of a V-valve 37 between standpipe and riser.

As hereinbefore described, other non-mechanical valves such as an L-valve, a J-valve, or mechanical valves, such as slide valves, can be used in place of the V-valve 37 without departing from the present embodi- ment.

It will be readily apparent to the skilled addressee that the device can operate over a range of solid flowrates and a range of pressure gains by vary¬ ing the pressure set points of the pressure controllers and by operating at different levels of solid in a standpipe.

Practical application for the invention include the general pneumatic conveying of solids (e.g. flyash, wheat and sand) and injecting solids into chemical reactors (e.g. gasifiers) which may be at pressures upto e.g. 10 atmospheres.

In a modified embodiment (not shown) the hopper 22 may be mounted above, and connected to, the upper end of the first standpipe 11. However, this arrangement requires greater headroom in the installation and so the use of a riser 14 between the hopper 22 and first stand¬ pipe 11, as shown, is preferred.

Various changes and modoifications may be made to the embodiment described and illustrated without depart- ing from the scope of the present invention as defined in the appended claims.