WO1992006030A1

WO1992006030A1 - Method for feeding bulk material into a pressurized space

Info

Publication number: WO1992006030A1
Application number: PCT/SE1991/000670
Authority: WO
Inventors: Erik Skog; Lars Chambert
Original assignee: Sydkraft Ab
Priority date: 1990-10-04
Filing date: 1991-10-04
Publication date: 1992-04-16
Also published as: SE468764B; SE9003172D0; SE9003172L

Abstract

Method for feeding bulk material into a space under overpressure, wherein the bulk material (20) is fed into a chamber (10) which is pressurized to a higher pressure, preferably corresponding substantially to said overpressure, and the material is fed into the space from the pressurized chamber. Simultaneously with or after the material being fed into the space, the volume of the chamber is reduced to a volume which is a fractional part of the normal volume of the chamber.

Description

TITLE: METHOD FOR FEEDING BULK MATERIAL INTO A PRESSURIZED SPACE

The invention relates to a method for feeding bulk material, especially fluffy bulk material, into a space under overpressure, e.g. for feeding of biomass, turf, saw dust, coal dust or energy forrest into a gasification vessel or another processing vessel. Normally in connection herewith the bulk material is fed into the vessel through a chamber having a sealable inlet for connection of the chamber to the surrounding air, and an outlet, which is also sealable, for connection of the chamber to the interior of the vessel. The chamber with the sealable inlet and the sealable outlet thus forms a lock. Usually the inlet is at the top and the outlet is at the bottom such that the bulk material can flow down into the chamber and can flow down into the vessel therefrom. The bulk material is fed into the chamber through the inlet, which then is connected to the surrounding air, i.e the low pressure side, while the outlet is closed. When the material has been fed into the chamber the inlet is closed, and the interior of the chamber, with the bulk material therein, is now under athmospheric pressure, which can be referred to as the lower pressure, in relation to the higher pressure in the vessel. The interior of the chamber having closed inlet and outlet is pressurized via a gas system to approximately the higher pressure existing inside the vessel, then the outlet is opened so that the bulk material is discharged into the vessel which is pressurized to the desired pressure level. After emptying the chamber the outlet is closed, and the chamber thus now has the higher pressure. However, the pressure in the chamber must be lowered again to the lower pressure, before the inlet can be opened in order that the chamber can again be filled with bulk material, and normally this is effected by the chamber being blown free with associated loss of pressurized gas.

In order to reduce the loss of gas the overpressure in the chamber can be utilized for pressurizing a system connected in parallel and having a similar lock which is operated with 180 degrees phase displacement so that half the pressure difference between the lower and the higher pressure can be utilized. The previously pressurized chamber must, however, be blown free in order to lower the remaining pressure therein to the lower pressure, and the gas loss is thus not quite eliminated by this alternative; it is reduced to approximately one half. Alternatively, the gas in the pressurized chamber may be evacuated by means of a compressor, which after cleaning of the gas, compresses it to at least the higher pressure for reuse.

It is very probable that the processing gas in the vessel, against which the bulk material is fed by the feeding system via the lock, mixes totally or partly with the pressurized gas in the chamber, which means that processing gas will be lost. If the processing gas is a toxic, flameable or expensive gas, this leads to serious consequences if there is no system for taking care of the gas leaving the chamber when it is being blown free. In the alternative with a compressor for recovering the gas, it is probable that the pressurizing gas will be diluted with processing gas, which can also lead to serious consequences depending on the type of processing gas used.

The amount of gas G (Mπtr/s), which is blown free or is being processed for reuse, depends on the volume V (m^**) in the chamber multiplied with the pressure difference between the higher pressure Pb and the lower pressure Pa (bar) . The volume V in turn depends on the flow of material m (kg/s), the density of the bulk material d (kg/πr) and the filling factor k. If the gas temperature is at normal condition then the following applies: G = (Pb - Pa) . k . m/d It is understood that the gas loss and costs connected therewith can be considerable in a processing plant dimensioned for commercial use. The purpose of the invention is to reduce the gas losses and thus the costs connected therewith, in feeding bulk material into a vessel under overpressure by applying the above illustrated procedure, the bulk material being fed through a lock. Thus, the invention relates to a method for feeding bulk material into a space under overpressure, wherein the bulk material is fed into a chamber, which is pressurized to a higher pressure, preferably substantially corresponding to said overpressure, and the material from the pressurized chamber is fed into the space. For achievement of said purpose the method has obtained the features of claim 1. For further explanation of the invention reference is made to the accompanying drawings, in which

FIG 1 in part figures a - f illustrates the method according to the invention when using a lock of a first embodiment, the lock being shown in different functional positions in a schematic longitudinal cross sectional view, FIG 2 in part figures a - f illustrates the method as in FIG 1 when using a lock of a second embodiment and in part figure g shows a cut along line g - g in part figure 2 b,

FIG 3 in part figures a - f illustrates the method as in FIG 1 when using a lock of a third embodiment,

FIG 4 in part figures a - g illustrates the method as in FIG 1 when using a lock of a fourth embodiment,

FIG 5 in part figures a - f, illustrates the method as in FIG 1 when using a modified embodiment of the lock in FIG 4, and

FIG 6 in a schematic longitudinal cross sectional view shows a further modified embodiment of the lock for use in the method of the invention in accordance with the principle which is illustrated in FIG 5.

In FIG 1 there is shown a lock comprising a vertical cylindrical chamber 10 with an inlet socket 11 on the side thereof which is spaced below the upper end of said chamber, said inlet socket being provided with a valve 12. The lower end of the chamber forms an outlet 13 to be connected to a space (not shown) under overpressure, for example a process vessel, and is provided with a valve 14. The chamber has an inlet 15 for pressurized gas provided with a shut-off valve 16. The valve 12 is thus the low pressure valve of the lock, which controls the communication between the chamber 10 and the athmosphere, and the valve 14 is the high pressure valve of the lock, which controls the communication between the chamber 10 and the pressurized space.

Above the inlet socket 11 there is attached at 17 a roll membrane of flexible material, for example rubber, a so called roll sock, which normally has the position shown in FIG 1 a - d but by means of a hydraulic system (not shown) connected to the upper end 19 of the chamber 10 can be supplied with fluid at the rear in order to take the position shown in FIG 1 e, wherein the roll membrane with fluid contained therein almost completely fills the interior of the chamber 10.

In the phase of the method according to the invention when the device according to FIG 1 is being used which is shown in FIG 1 a, the valve 12 is open and the valve 14 is closed. The chamber 10 is thus separated from the high pressure side (the pressurized space) and communicates with the low pressure side (the atmosphere) . The pressurized gas valve 16 is closed. The lock is now ready to receive bulk material, and according to FIG 1 b such material 20 is supplied through the inlet socket 11, the bulk material being able to flow into the chamber. When a suitable amount of bulk material 20 has been supplied to the chamber 10, FIG 1 c, the valve 12 is closed in order to separate the chamber from the low pressure side, and then the valve 16 is opened for the supply of pressurized gas to the chamber 10 in order to increase the pressure in the chamber, preferably substantially to the same pressure level as that existing in the pressurized space which is connected to the lower end 13 of the chamber 10. When thus the bulk material has been pressurized to the desired pressure, the valve 14 is opened, and the bulk material can flow down into the space which is connected to the lower end 13 of the chamber 10, said space being under substantially the same pressure as the pressure in the chamber, FIG 1 d.

Simultaneously with or immediately after the emptying, the volume of the chamber 10 is reduced to the minimum volume thereof by pressing the roll membrane 18 into the chamber 10 by means of hydraulic fluid, the pressure thereof being somewhat higher than the higher pressure existing in the pressurized space which is connected to the lower end of the chamber, said hydraulic fluid being pressed into the chamber 10 such that the roll membrane with fluid therein almost entirely fills the chamber 10, as shown in FIG 1 e. Since the fluid in principle is incompressible, the roll membrane will not change position thereof even if the pressure in the chamber 10 is changed. The gas in the chamber 10 is thus pressed into said pressurized space through the open valve 14 or through a gas system connected to the chamber 10, by means of the roll membrane. When the valve 14 has been closed and the gas system, if any, has been disconnected from the chamber, the fluid is again evacuated from the rear of the roll membrane 18, the volume of the chamber 10 being increased, FIG I f, which means that the pressure in the chamber 10 simultaneously will be lowered. When the pressure has reached the level of the low pressure side or another predetermined lower pressure level, the valve 12 can be opened. Alternatively, the lower pressure may be maintained by a gas system connected to the chamber 10 during the period when the volume of the chamber 10 is increased to its largest volume by withdrawal of the roll membrane 18. When this has been done the valve 12 is opened. The cycle has then returned to the first moment, FIG l a, and further bulk material can now be supplied to the chamber 10.

At the lock shown in FIG 2 the same effect is achieved as in the embodiment according to FIG 1 with a "stationary" roll sock 21 which all the time is situated within the chamber 10. It is partly attached along its length to the inside surface of the chamber wall at the side of the chamber opposite to the socket 11, and in the upper part thereof there is a filling body 22. The roll sock can be filled with fluid under pressure through a supply conduit 23. The roll sock normally is substantially emptied so that it lies close to the wall of the chamber 10 and thus occupies a small volume, FIG 2 a - d and FIG 2 f and 2 g. Bulk material 20 is supplied to the chamber 10 and is emptied therefrom into the vessel connected to the chamber in the way shown in FIG 2 b - d, according to the same principles as earlier described. When the material has been emptied from the chamber and the volume thereof is to be reduced, the roll sock 21 is filled with fluid under pressure, the valve 14 being opened, and then this valve is closed, FIG 2 e, and the fluid is evacuated from the roll sock in order to increase the volume of the chamber 10, FIG 2 f, and to prepare the chamber for the reception of a new load of bulk material.

In the variant of the method according to the invention, which is shown in FIG 3, a lock is used, wherein the inlet valve 12 is provided at the upper end of the chamber 10 and the roll membrane is replaced by an elastic lining 24 on the inside surface of the side wall of the chamber 10. The lining can have the form of a tube or be arranged as a number of sections which are distributed along the side wall of the chamber. Fluid can be supplied between the lining 24 and the side wall of the chamber 10 from a hydraulic system through a conduit 25 in order that the lining will expand into the space of the chamber and together with the fluid volume inside the lining will fill said space. The method is in principle applied as described in connection with FIG 1. With the valve 12 open and the valve 14 closed according to FIG 3 a, the bulk material 20 is supplied to the chamber 10 according to FIG 3 b. The valve 12 is then closed and the chamber 10 is pressurized according to FIG 3 c. After the pressurizing, emptying is effected according to FIG 3 d by the valve 14 being opened. After the emptying the volume of the chamber 10 is reduced by the lining 24 being brought to expand by supplying fluid under pressure, FIG 3 e, whereupon the valve 14 is closed. The lining may then return, and when the lower pressure has been reached, the valve 12 is opened, FIG 3 f, whereupon the lock is ready to receive bulk material again according to FIG 3 a. Also in the embodiment according to FIG 3 a gas system connected to the chamber 10, can be provided to control the pressure in the chamber 10 during expansion and contraction, respectively, of the lining. According to FIG 4 the lock is provided with a piston 26 which is displaceable within the chamber 10. This piston works in principle in the same way as a roll membrane according to FIG 1 but must of course be provided with a seal, partly indicated at 27, for sealing between the piston and the cylinder (the chamber 10). The piston is withdrawn from the inlet socket 11 in FIG 4 a, and the valve 12 is open. After bulk material having been supplied, FIG 4 b, the valve 12 is closed and the piston 26 is moved downwards, FIG 4 c; the piston may be used to compress the bulk material in the chamber 10 by this movement. After the chamber 10 having been pressurized, the valve 14 is opened and the material flows down into the pressurized space while the piston follows and fills the chamber 10, FIG 4 d. When the valve 14 has been closed the piston 26 is withdrawn, FIG 4 e and f, whereupon the valve 12 can be opened, and the lock is ready to receive bulk material again. Also in this case there may be provided a gas system connected to the chamber for pressure control in the chamber 10. The pressurization of the chamber 10 can be effected via the sealing system of the piston in order to blow the piston and the sealing system thereof free from bulk material.

According to FIG 5 the lock is modified by the valve 12 being left out and the piston 26 having taken over the function thereof. Thus, the inlet socket 11 is open in FIG 5 a and b, while it is closed by means of the piston in FIG 5 c - f, in order to be opened again when the piston is withdrawn from the position in FIG 5 f to the position in FIG 5 a. The method is applied as earlier described for the embodiment according to FIG 4.

Two pistons 26A and 26B, which are displaceable towards and away from each other may be provided according to FIG 6, the chamber 10 being inclined and having also an outlet socket 28. When the chamber 10 is being filled, the outlet socket 28 is closed by means of the piston 26B, while the inlet socket is open by being uncovered by the piston 26A. When the chamber 10 is being emptied the outlet socket is open, and when the pressure is being increased and decreased the two sockets are closed by means of the respective pistons.

The constructive details of the lock may of course be varied and the schematically described embodiments herein only serve to illustrate more fundamental differences in the constructive embodiment of the device which is used for application of the method according to the invention which, however, in principle is the same and in accordance with the inventive concept irrespective of the device used.

Claims

1. Method for feeding bulk material into a space under overpressure, wherein the bulk material is fed into a chamber which is pressurized to a higher pressure, preferably corresponding substantially to said overpressure, and the material is fed into the space from the pressurized chamber c h a r a c t e r i z e d in that the volume of the chamber simultaneously with or after the material being fed into the space, is reduced to a volume which is a fractional part of the normal volume of the chamber.

2. Method according to claim 1, wherein the reduction of the volume is effected by a flexible and/or elastic element being brought to fill the chamber.

3. Method according to claim 2, wherein the element is brought to fill the chamber by the element being influenced by means of a hydraulic pressure.

4. Method according to claim 1, wherein the reduction of the volume is effected by a piston being brought to fill the chamber.

5. Method according to claim 4, wherein the piston, when filling the chamber, closes an inlet for feeding the bulk material into the chamber.

6. Method according to claim 5, wherein a second piston together with said piston is brought to fill the chamber and the second piston then closes an outlet for discharging the bulk material from the chamber.

7. Method according to claim 5 or 6, wherein the bulk material is compressed in the chamber by means of the piston or the pistons, respectively.

8. Method according to any of claims 5 - 7, wherein the pressurization of the chamber is effected via sealing systems for the piston or the pistons, respectively, in order to clean the sealing systems by blowing.