AU747579B2

AU747579B2 - Method and device for feeding granular solid substances into pressure systems or pressure reactors

Info

Publication number: AU747579B2
Application number: AU60808/99A
Authority: AU
Inventors: Bernd Krodel
Original assignee: VEAG Vereinigte Energiewerke AG
Current assignee: Vattenfall Europe Generation AG and Co KG
Priority date: 1998-09-10
Filing date: 1999-09-10
Publication date: 2002-05-16
Anticipated expiration: 2019-09-10
Also published as: EP1113972B1; DE19843255A1; AU6080899A; HUP0103911A2; DE59905870D1; PL346537A1; EP1113972A1; WO2000015523A1; HUP0103911A3

Description

Method and device for feeding granular solid substances into pressure systems or pressure reactors The invention concerns a method and a device for feeding granular substance for pressurised preparation and processing processes with changing the gas atmosphere when entering into the pressurised system. The invention is particularly suitable for use in coal-fired power stations to feed the coal to steamfilled pressurised drying reactors.

It is known that the feeding of solid substances into preparing or processing reactors operating under pressure is carried out in a granular to fine-granular form. The feeding systems are matched to suit the properties of the solid substance and its pouring properties on the one hand and the pressure and temperature differences which have to be overcome on the other, as well as the magnitude of the conveying current. Based on the basic technological principle the large number of feeding systems known so far is reduced to the groups displacement systems chamber locks cell wheel locks packing screws extruders tube chain conveyors.

Displacement systems, generally comprising cylindrical containers to receive the material and a piston moving therein, like those described in DE 84 30 90, DE 12 490, DE 245 414, DE 38 13 899 operate intermittently and only in conjunction with ball valves, cone valves or parallel slide gate valves as additional locking elements for the working gases or working liquids. From the point of view of the pressurised system to be charged a quasi-continuous feeding can be achieved only by means of a multi-stage or multi-linear arrangement.

A suspension feed accomplished by means of thick-substance piston pumps represents a practical solution wherever the fluid phase of the suspension does not have a disrupting influence on the entire process.

If used for the feeding of fuel having high moisture content, like brown coal, this solution would have a disadvantage since the bottom thermal value is further reduced and the efficiency of the process of energy transformation would be additionally adversely affected.

Chamber locks known from the blast furnace technology and coal gasification are also characterised by an intermittent mode of operation and to achieve a quasicontinuous feed for the respective pressurised system they require a multi-path construction that is technology and cost intensive. Typical solutions of this are described in DE 169724, DE 482402, DE 862429, DE 1903539, DE 260754, DE 3619141, DE 3205321, DE 4114680, DE 3311655, DE 3410721.

The cell wheel locks, acting as "rotating" chamber locks, allow a continuous feed.

However, to ensure the discharge of the cells so far they have been suitable only for applications when the pressure differential is low (up to 300 kPa) and together with good flow behaviour (DE 1049303).

The mechanical, dry feed by means of packing screws, known as Fuller- or M1ller-pump, in the feed stations of pressurised pneumatic conveyors, preferably operating with pressurised air, pressurised nitrogen or inert, compressed flue gases, just overcomes counterpressures up to a maximum of 500 kPa. However, in this case the material conveyed or fed has to be dry at least on the surface.

This system is not suitable when using, for example, fuels with high moisture content, like brown coal. As it is known from DE 1442742, DE 2249453 and DE 29043321, the packing screws work against shuttle flaps or against sealing peeling heads or milling heads positioned downstream. A packing screw, mounted on both sides, is known from DE 215989.

Although extruders as packing screws with continuously reducing transport crosssection are suitable to overcome very high pressure differentials (up to 120 MPa and up to 100 t/h throughput), their use is limited to dry and powdered material, so that no compacting of the fine-granular solids occurs during compression.

Tube chain conveyors are known that are equipped to overcome the pressure differentials with a lock gas displacement by means of feeding pressurised water into individual cells of the empty tube section. As feeding system this solution is not suitable, for example, for fine-granular brown coal, because of the tendency of this solid substance to caking and adhesion will not be reduced, but rather increased.

The analysis of the solutions known so far shows that currently there are no suitable solutions for an unlimited continuous feeding of surface-moist solid substances, like, for example, granular brown coal, into pressurised systems at an absolute pressure between 500-2000 kPa. The feed of this special fuel is even more difficult into pressurised system reactors, wherein the pressurised system is built up only by slightly overheated steam and the flow rates are in the order of 30-200 t/h.

The object of the invention is to enable to feed granular and surface-moist substance, like, for example, brown coal, in the form of raw fine coal, directly and continuously into pressurised systems, while the gas atmosphere in the pressurised system is generally different from that outside of the pressurised system, the pressure differential to be overcome is 500 kPa and the flow rate is at least 25 t/h.

According to the invention this will be achieved by the patent claims, wherein the granular substance is fed to the pressurised reactor with a tube chain conveyor, whose forward and return strands are used for the feeding both from the drive side and from the opposite situated side with a tensioning station and both conveying tubes have a discharge socket situated longitudinally approximately in the middle, the sockets subjected directly to the pressure of the pressurised reactor that is being fed. Atmospheric pressure prevails on both inlet sockets of the forward and return strand. In the feeding direction past the inlet socket and in both empty sections, in each case before the reversing of the chain, there are tube sockets to discharge slightly pulsating quantities of escaping gas that have been relieved in both sections of the conveyor tubes approximately up to the

TLN

4 ambient pressure. Whereas in both conveyor tube sections the granular substance encounters two types of resistance of the escaping gas and thus itself partly contributes to the pressure sealing, all conveyor discs have flexible sealing rings (preferably leather collars) that by virtue of the higher gas pressure on one side of the disc are slightly pressed against the conveyor tube, so that the flow of escaping gas is minimised especially in the two empty tube sections (tube sections not filled with material).

The tube sockets for the escaping gas of the empty tube sections are connected via the shortest path with the tube sockets for the escaping gas of the section of the filled tubes by means of a tube and thus connected to a cloth filter, in which the very fine grain carried away is deposited and returned to the main conveying current.

The pressure pulses of the current of the escaping gas from the empty tube sections serve the purpose of cleaning the filter elements.

The solution according to the invention is explained in detail based on an embodiment. Shown is in: Fig.1 the pressure-tight tube chain conveyor, longitudinally sectioned, Fig.2 the arrangement of the sliding and sealing collars on the main conveyor disc, Fig.3 lateral material feed into a pressurised reactor, sectioned.

The tube chain conveyor and feeding equipment 1 that is enclosed against excess pressure and simultaneously carries out the separation of gas atmospheres has, in contrast to the usual tube chain conveyors, a pressure-proof connecting piece 4 arranged in the middle with the conveyor tube discharge positions 11 and 12, which is directly attached by its flange to the upper part (not illustrated) of the pressurised reactor. The central connecting piece 4 is connected to the tensioning station 3 and the drive station 2 via the conveyor tubes 5 and 7, including the empty tubes 6 and 8. The conveyor tubes 5 and 7 have sockets 9 and 10 for the inlet of the solid substance as well as sockets 17; 18 provided at a short distance, respectively, behind them, to discharge the escaping gas. Sockets 19; 20 to discharge the escaping gas are provided also on the empty tubes 6; 8; in this case at a small distance from the chain reversing stations. The reversing stations 2; 3, the discharge station 4 and the conveyor tubes 5; 6; 7; 8 accommodate the conveyor chain 22 provided with the conveyor discs 21. The tubes 13 and 14 connect the discharge positions 19; 20 of the escaping gas with the dust filters 15; 16 for the escaping gas that are connected directly to the discharge positions 17; 18, respectively, for the escaping gas.

Fig.2 shows a single conveyor disc 21 with flexible collar rings 23, which rings, due to the higher pressure of the gas 28 occurring on this side of the disc, is pressed sufficiently strongly against the inside wall of the empty tube 6; 8, while no gas 24 must escape through the annular gap 25 to ensure a gradual pressure reduction in the direction of the movement of the chain between the discharge combination 4 and the sockets 19; 20 for the discharge of the escaping gas. In the actual conveying sections 5; 7 the sealing effect of the flexible sealing collars is replaced by the solid substance filling itself, while a current of the escaping gas to lock the different gas atmospheres is necessary in these conveying sections also. If a steam atmosphere or an atmosphere of other easily condensable gases is present in the discharge element 4, then the sections 5; 6; 7; 8 are constructed with coaxial tubes, whereby between the inside conveyor tube and the outer tube 26 a heating medium (not indicated in detail) is conducted.

This indirect heating prevents the condensation of the escaping gas and, on the other hand, contributes to the pre-heating of the substance to be fed. The thermal insulating layer 27 reduces the thermal losses, that are equalised by the heating medium, but not by the currents of the escaping gas.

Fig.3 shows a pressure-tight conveying and feeding device on the lateral container wall that conveys into the pressurised reactor 30, in this case as a simple, single-tube feeder, since due to the size of the diameter of the pressurised reactor the return strand cannot be simultaneously used as a second or parallel feeder. A further simplification, when compared with the device according to Fig.l, is that the reversing 3 of the conveyor chain, situated in the pressurised reactor, is simultaneously the discharge position 11 of the feed equipment. The disadvantage of the halved feed capacity is compensated for by the advantage of an improved fluidity, for example of the raw brown coal, due to the fact that the active conveying region (inside wall of the tube, discs, chain links) is "covered" with dry dust, that is introduced together with the current of escaping vapour 29 into the empty return strand for a pressurised drying process, so that further moisture, in particular on the surface of the coal grain, will be rendered harmless for adhesions and caking ons. This device according to the invention makes firstly feasible a "real" continuous feed of the bulk material having a large proportion of moisture, e.g. of raw fine brown coal, into working processes operating under pressure, also into energy exchange and transformation processes operating under pressure, while the counterpressure is 500 kPa or more, consisting mostly of gases and mixtures of gases other than air.

Further advantages arise from the fact that excess pressure is present only in the conveyor tubes, the reduction of the pressure (Fig.l) takes place in the direction of drive and reversing stations which themselves are not subjected to excess pressure, that the discharge in the middle results in an almost symmetrical pressure load of the conveyor/feed equipment, the feeding of the media and the sealing of the pressure are carried out in the one and same equipment, the doubled feed capacity is achieved at the same chain speed (0.2-0.3 m/sec) when compared with tube chain conveyors used until now, the purification of the escaping gas, the utilisation of the escaping gas is also assured, the enclosed and dust-tight system has a high degree of fire and explosion safety.

Claims

1. A method for feeding granular solid substances into pressurised systems or pressurised reactors, wherein always a gas atmosphere other than air is present, characterised by that the small-grained substance is fed continuously and with its mass current controlled to a tube chain conveyor directly connected to the pressurised reactor (30) and the pressure sealing between the tube inlets 10) and tube discharges (11; 12) is carried out on the one hand by the conveyed substance itself and by flexible sealing collars (23) provided on one side of the chain conveyor discs (21) on the other, which collars are pressed against the inside wall of the conveying tube by the higher gas pressure on one side of the disc each time when moving in the empty tube but at the same time allow a current of escaping gas, due to its gradual partial relieving on each passing-through gap (25) within the active total conveying path the total pressure differential to be overcome is equalised.

2. A method according to claim 1, characterised in that both the forward and the return strand are used for feeding by the tube chain conveyor

3. A method according to claim 1, characterised in that with the aid of the escaping gas both a direct heating of the conveying sections 7) filled with the granular substance and a pre-heating of the substance to be fed is carried out indirectly by heating the conveyor chain (22) in both empty tube sections 8).

4. A device for feeding granular solid substances into pressurised systems or pressurised reactor, characterised in that a tube chain conveyor known per se, has a pressure-tight construction, wherein the main conveyor discs (21) are provided with flexible sliding and sealing collars (23) for sealing the annular gap (25) and/or the partial annular gap between the disc (21) and the conveyor tube 7) the discharges (11; 12) are provided longitudinally in the middle and, viewed in the direction of transport, after the region of the material feed 10) and connecting sockets (19; 20) are provided in the empty tube sections 8) before the reversing 3) of the chain.

A device according to claim 5, characterised in that the sliding and sealing collars (23) are provided on one side of the main conveyor discs (21).

6. A device according to claim 4, characterised in that cloth filters (15; 16) are provided on the tube sockets 3). 3 pages of drawings List of reference numerals 1 Tube chain feeder 2 Drive and reversing station 3 Tensioning and reversing station 4 Pressure-proof discharge station First feed tube 6 First empty tube

7 Second feed tube

8 Second empty tube

9 First material feed Second material feed 11 First material discharge 12 Second material discharge 13 First connecting pipe for escaping gas 14 Second connecting pipe for escaping gas First dust remover for the escaping gas 16 Second dust remover for the escaping gas 17 Connecting socket for the escaping gas 18 Connecting socket for the escaping gas 19 Connecting socket for the escaping gas Connecting socket for the escaping gas 21 Main conveyor disc 22 Conveyor chain link 23 Sealing collar 24 Escaping gas Annular gap 26 Coaxial tube section 27 Heat insulation 28 Pressurised gas 29 Vapour charged with gas Pressurised reactor