AU2011101245A4 - Low-rank coal handling system - Google Patents

Abstract

The present innovation provides a safe and environmentally friendly system for packaging and transporting dried low-rank coals over long distances. The invention comprises purging the dried coal using inert gases and packaging the coal 5 powder/particles/briquettes in a closeable container, such as a flexible bulk container. The container is squeezed to expel the carried gas, and hence achieving dense packaging. The containers of the low-rank coal powder/briquettes using the present invention can be transported by road and rail trucks, and by bulk shipping or container ships over long distances with reduced/minimized risk of spontaneous combustion and water re 10 absorption, The system also substantially prevents dust pollution generated during handling of dried low-rank coals. 0 o I-i 02 o tao cri C-) C.) Ca 0-) a, c'i bfl a-) C)

Description

LOW-RANK COAL HANDLING SYSTEM Field of the Invention This invention relates to a system, including a process and apparatus, for handling of dried low-rank coals for storage and/or transport. The invention has been particularly 5 developed as a system for packaging such coal for storage and transport in discrete packaged containers, Background of the Invention There are vast resources of low-rank coal coals including brown coal (lignite) and sub-bituminous coal worldwide. The resources of brown coal in Victoria, Australia, 10 present a significant proportion of the world's brown coal endowment, Only small quantity of brown coal is currently used for electricity generation at a few power stations, while there are increasing demands for the coal resources from Asian countries, especially, China and India. The high water content (which can be up to 70% by weight as mined) and high reactivity of brown coal have to date made its export unsafe and 15 commercially unattractive. The technical challenges for exporting brown coal include the development of cost-effective drying and briquetting processes, safe transport of the dried brown coal briquettes/powder/particles over long distance, and handling of dried brown coal without dust pollution. While various drying technologies have been developing to remove the water content in brown coal, no safe and environmentally 20 friendly technique has been developed and successfully used for the storage, handling and the long distance transportation of the dried brown coal powder/particles. Low-rank coals are naturally types of younger coals. Their strong tendency of the spontaneous combustion makes raw and dried low-rank coals very dangerous to transport over long distance. In currently known brown coal processes, crushed raw brown coal is 25 dried using various technologies including steam fluidized bed drying, steam tubular drying and/or flash heat drying, and so on, The size of the dried brown coal particles/powder varies with the drying technology used. The dried particulate coal is then formed into briquettes under high mechanical force using pressing machines such as ram extrusion and roller presses. The briquetting process largely reduces the degree of 30 tendency for spontaneous combustion and increases the weather resistance during transportation and storage. However, the brown coal briquettes are still classified as a self-heating material by international maritime authorities and can only be transported under certain restrictions.

In addition to the transportation safety issues, the coal dust generated during loading and unloading has caused severe environmental concerns including respiratory damage to workers and nearby residents, and environmental pollution from settling dust. In many applications, the dried brown coal is to be consumed as pulverized coal, such as s injection coal for blast furnaces, gasification coal and thermal coal used for power generation. For such applications, the direct transportation, enabling immediate utilization, of dried brown coal in power/particle form is desirable. However, because of the strong tendency of spontaneous combustion and the coal dust pollution during the transportation, there is currently no effective technique used to transport the dried brown 10 coal in powder/particle form. In addition, even using the briquettes of brown coal, there is still significant amount of coal dust produced from various stages of the handling and transportation, does not overcome the issues with the transportation safety and dust pollution. Transporting briquettes also requires significant energy consumption to pulverize the briquettes if powder/dust is required by the final consumer, e.g. for blast 15 furnace injection. Australian Innovation patent application AU 2009100667 describes a concept of vacuum packing grus, dried coal and Brix. However, no detail of the process and apparatus is described beyond the general concept. The above references to and descriptions of prior proposals or products are not 20 intended to be, and are not to be construed as, statements or admissions of common general knowledge in the art in Australia. Object of the Invention It is an object of the present invention to provide a process and apparatus for handling low-rank coals, particularly brown coal, which can enable relatively safe and 25 easy storage and/or transportation. Low-rank coals can have high water content (up to 70 wt%), making it uneconomic to transport such untreated coals over long distances. At present, the raw low-rank coal needs to be dried and pressed to form briquettes using high mechanical force in order to achieve structural integrity and good weather resistance and prevent 30 spontaneous combustion during storage and transportation. There is no appropriate technique used to store, handle and transport dried low-rank coal powder/particles in a safe manner. The present invention has a preferred object to provide a safe and environmentally friendly system for packaging and freighting dried low-rank coals in 2 different particulate forms of briquettes, particles and/or powder. Summary of the Invention According to a first aspect of the invention there is provided a process for handling a low-rank coal, such as brown coal, for storage and/or transport, including the 5 steps of feeding a dried low-rank coal with a relatively low water content in a particulate form (which includes in the form of powder, fines, grus, granules, grains, pellets, briquettes and/or blocks) to a displacement station; supplying a non-oxidi2ing gas to the fed coal in particulate form at the displacement station so as to displace a substantial proportion of air mixed with the fed coal with the non-oxidizing gas and thereby 10 produce a treated coal having a reduced oxygen content of the gas mixed with the particulates; at least partially filling a closeable container with the treated coal; increasing the packing density of the treated coal by reducing the gas space between the coal particulates in the container; and closing the container for storage and/or transport of the treated coal in the container so as to maintain a reduced oxygen content therein. 15 Preferably the displacement station has a displacement zone through which the coal in particulate form is passed and preferably the non-oxidizing gas is introduced into the displacement zone to create a counter flow direction of gas movement whereby the non oxidizing gas displaces and substitutes for a substantial proportion of air within the coal passing through the displacement zone. The parameters of the coal and its flow through 20 the displacement zone and parameters of the introduction and flow of the non-oxidizing gas are preferably controlled to result in substantial fluidization of the particulate coal passing through the displacement zone, A body or bed of the fed coal particles may be created in the displacement zone, and gas is introduced from beneath so as to create the fluidization. 25 Preferably the closeable container is a closeable package which can be handled as a discrete article in its storage and/or transportation. In this process, preferably the process includes feeding the treated coal with the reduced oxygen content from the displacement station to a separate packaging station where the at least partial filling of the closeable container occurs. Preferably the flow path of the treated coal being fed from the 30 displacement station to the packaging station and the path of the treated coal within the packaging station entering the closeable container is maintained substantially closed so that no substantial quantity of ambient oxygen is reintroduced into the coal to displace non-oxidizing gas therein. 3 The closeable container preferably is substantially impermeable to gas and wherein the step of closing the container comprises sealing the container so that the resulting sealed container is substantially impermeable to gas. Although a flexible container is the preferred container, it is also within the broad 5 invention to use a rigid closeable container such as a large box, sealable shipping container, or even a closeable and sealable compartment such as a ship's hold for bulk particulate materials. The process preferably further includes the step of increasing the density of treated coal in the container by reducing the gas space between the coal particulates after 10 introduction into the closeable container. The step of increasing the density may comprise compacting and/or settling of the treated coal within the closeable container. The process may include the further step of adding more treated coal to the container after the step of compacting and/or settling and thereafter repeating the compacting and/or settling step, The compaction step may comprise pressing the container and/or the 15 treated coal supplied into the container, including by means of a selectively moveable pressing member to mechanically compact the coal in the container and by applying a partial vacuum to the container so that ambient air presses the container walls inwardly to compact the coal. The settling step may comprise vibrating or lifting and dropping by a short distance the container to settle and compact the coal by gravity. 20 Preferably the non-oxidizing gas includes carbon dioxide or nitrogen or treated flue gas or mixtures thereof Carbon dioxide or treated flue gas may be readily available if the plant includes a process in which the fuel is being burned to supply heat for the drying of raw brown coal, or if the plant utilizing the invention is near a power generation facility where coal from the same source is being burned for electric power 25 generation. The oxygen content of the gas mixed with the treated coal emerging from the displacement station preferably is less than about 13% by volume, and most preferably is less than or equal to about 7% by volume. Such oxygen levels will very substantially reduce the risk of spontaneous combustion. 30 According to a second aspect the invention provides apparatus for handling of a dried low-rank coal, such as brown coal, for storage and/or transport, the apparatus including: means for feeding a dried low-rank coal with a relatively low water content in a 4 particulate form (which includes in the form of powder, fines, grus, granules, grains. pellets, briquettes and/or blocks) to a displacement means; gas supply means associated with the displacement means and operative to supply a non-oxidizing gas to the fed coal in particulate form in the displacement means so as to displace a substantial proportion of 5 air mixed with the fed coal with the non-oxidizing gas and thereby produce a treated coal having a reduced oxygen content of the gas mixed with the particulates; filling means operative to at least partially fill a closeable container with the treated coal; means for increasing the packing density by compacting/settling the treated coal within the closeable container; and means for closing the container for storage and/or transport of 10 the treated coal in the container so as to maintain a reduced oxygen content therein, The displacement means preferably includes a displacement vessel or tower through which the particulate coal enters under gravity and preferably the gas supply means comprises multiple gas introduction means distributed in the displacement vessel or tower to introduce the non-oxidizing gas generally throughout the flow area of the 15 particulate coal. Preferably the closeable container is a closeable package which can be handled as a discrete article in its storage and/or transportation and wherein the filling means comprises a packaging apparatus separate from and downstream of the displacement means and to which the treated coal is fed in a closed path inhibiting introduction of 20 oxygen into the flow and to displace non-oxidizing gas. The packaging apparatus may include means to increase the density of the treated coal fed into the container by reducing the gas content of the treated coal within the container. The means to increase the density may comprise means for compacting and/or settling treated coal introduced into the container, and the apparatus is preferably further operative to introduce more 25 treated coal into the container after the means to increase density has been operated to compact or settle coal within the container, the increase in density and addition of more coal being repeated at least once until a predetermined amount of treated coal has been introduced into the container. Preferably the non-oxidizing gas includes carbon dioxide or nitrogen or treated flue 30 gas or mixtures thereof The closeable container is preferably substantially impermeable to gas and preferably the means for closing the container is operative to seal the container so that the resulting sealed container is substantially impermeable to gas. 5 The oxygen content of the gas mixed with the treated coal emerging from the displacement means preferably is less than about 13% by volume, and most preferably is less than or equal to about 7% by volume, The present invention in its preferred embodiments can provide a safe and dust-free 5 technique for transporting dried low-rank coals having a tendency of spontaneous combustion and the characteristic of generating dust during storage, handling and long distance transportation, Such materials include, but are not limited to, dried brown coal (lignite) and sub-bituminous coal powder/particles/briquettes. The preferred system of the invention uses the inert or non-oxidizing gas to displace or purge oxygen carried in 10 the fed dried coal and compacting and/or settling the container with treated coal powder to expel gas, hence minimizing or reducing the voids in the packaged coal. The oxygen concentration in the container will be minimized to a level that should not enable spontaneous combustion. The container can be tightly enclosed and little or minimal ambient air can enter the container over a long period of storage and transportation. The 15 container can be transported by normal road and rail trucks and by bulk or container shipping methods to destinations. The handling of closed containers only can effectively avoid the generation of coal dust pollution. Because the present invention provides a safe technique for the handling, transport and storage of the dried low-rank coals, it can effectively reduce fire, explosion and dust hazards at the production sites, transporting 20 vehicles and consumer sites. Description of preferred embodiments of the invention Possible and preferred features of the present invention will now be described with particular reference to the accompanying drawings. However it is to be understood that the features illustrated in and described with reference to the drawings are not to be 25 construed as limiting on the scope of the invention. In the drawings: Fig. 1 is a schematic overall view of a system of coal handling according to one embodiment, and Fig. 2 is a schematic side sectional view of apparatus used in the system of Fig, 1, 30 The system in the drawings has a displacement means comprising an inert gas purging tank 2 and a filling means comprising a packaging apparatus 7 with package squeeze function, Dried low-rank coal from a drying process, which is not included in the present invention, is fed into the purging tank 2 through a conveyer 1, The inert gases, including 6 (but not limited to) nitrogen and/or carbon dioxide and/or treated flue gas is supplied into the purging tank 2 through specially designed gas distributor 5 such as a manifold. Carbon dioxide or treated flue gas may be readily available if the plant includes a process in which the fuel is being burned to supply heat for the drying of raw brown coal, or if 5 the plant utilizing the invention is near a power generation facility where coal from the same source is being burned for electric power generation. The treatment of the flue gas to make it more acceptable for use in the present system may include removal or reduction of unwanted components, such as water. The gas distributor is designed to provide uniform gas distribution across the entire section of the purging tank. The gas 10 flows in a counter flow direction through the coal bed to purge air carried by the fed coal. Ideally, the bed of coal powder/particles 3 is slightly fluidized to achieve a better purging effort. An oxygen analyzer 4 measures the oxygen concentration in the purging tank. The oxygen concentration is controlled preferably at below 13%, ideally, below 7% e.g. by adjusting the gas flow rate and/or coal feed rate, The purging gas vents through a cyclone 15 6 after removing the carried coal particles. The collected fine coal dust from cyclone 6 is returned to the tank 2. The treated coal with reduced or minimum oxygen content in gas phase is then fed to a flexible bulk container 8 at the packaging apparatus 7. The flexible coal bulk container 8 can be made of any suitable material such as thick woven polyethylene, polypropylene or PVC, which 20 is internally coated or have an impermeable internal layer to make it substantially impermeable to gas so as to exclude the ambient moisture and air from the coal. The coal container for example can have a capacity of holding 1-3 tonnes of coal. An electronic weighing device 16 can be located underneath the packaging platform, which can initiate a stop of the coal feeding when the package reaches the preset weight. 25 The container is closed by any suitable means (including a manual process) and is moved from the packaging apparatus by a conveyor 9 such as a roller conveyer, sandwich belt conveyor and so on. Multiple coal containers can be lifted in a group to a storage area, and later loaded onto road or rail trucks for transport to a shipping terminal. The coal containers can be transported either by a bulk cargo or loaded into conventional 30 shipping containers, hence enabling shipping by container ships. Fig. 2 illustrates more detail of the packaging apparatus 7, The air carried in the fed dried low-rank coal is purged by the inert gases, such as nitrogen and/or carbon dioxide, and/or treated flue gas in the purging tank 2, The oxygen concentration is hence 7 reduced to below 13%, ideally below 7%. The treated coal with the lowered oxygen concentration discharges from the purge tank 2 through a rotary control valve 10, The treated coal is fed in a closed path to exclude re-introduction of oxygen to a flexible bulk container 8 through a screw feeder 11. Alternatively, for the coal powder/particles with 5 good flowablity and pellets/briquettes, the material can also be fed directly into the container through a suitable and controllable valve without a screw feeder, The container has two openings, one on the top and one at the bottom, which are used for feeding and later discharging coal, respectively. The packaging device has hanging hooks 14 to hang the bulk container. The empty container can be purged throughout by the inert gas before 10 feeding the treated coal. The feeding speed is controlled by the rotational speed of the screw feeder 11 or a controllable valve, During the course of feeding and at the end of feeding cycle, the container is squeezed several times by a squeezing member such as a block 12 that is driven eg. by pneumatic or hydraulic rams 13. The squeezing block also has a circular gas-venting channel 15 surrounding the feed chute through which the coal 15 is supplied into the container, and which contains a filter to prevent the coal powder/particles to escape, Squeezing the container can effectively expel a significant proportion of the gas in the container through the venting channel 15, hence reducing the voids in packaged coal powder and increasing the overall packing density. The venting channel 15 is connected to a vacuum system to aid the exhaustion of expelled gas. The 20 densely packed material can also help prevent the penetration of the external air during long periods of storage and transportation and thus eliminating or at least substantially reducing the possibility of spontaneous combustion. The container also provides a good weather seal for the treated coal, particularly to inhibit moisture re-absorption. There is an electronic weighing device 12 underneath the package platform to weigh the 25 container, The feeding of the container is stopped once the preset weight is reached. The top opening of the fully filled coal container is then closed and sealed. The container is moved away from the packaging device by a conveyor such as a roller conveyor or sandwich belt conveyor. It will be seen that the prefeted embodiments of the system of the invention can 30 provide safe and environmentally friendly technique for packaging and freighting dried low-rank coals in different forms of powder, particles and briquettes. It is to be understood that various alterations, modifications and/or additions may be made to the features of the possible and preferred embodiment(s) of the invention as 8 herein described without departing from the spirit and scope of the invention. 9

Claims (18)

1. A process for handling a low-rank coal, such as dried brown coal, for storage and/or transport, including the steps of: feeding a dried low-rank coal with a relatively low water content in a particulate 5 form (which includes in the form of powder, fines, grus, granules, grains, pellets, briquettes and/or blocks) to a displacement station; supplying a non-oxidizing gas to the fed coal in particulate form at the displacement station so as to displace a substantial proportion of air mixed with the fed coal with the non-oxidizing gas and thereby produce a treated coal having a reduced oxygen content of 10 the gas mixed with the particulates; at least partially filling a closeable container, such as a flexible bulk container, with the treated coal; increasing the packing density of the treated coal by reducing the gas space between the coal particulates in the container; and 15 closing the container for storage and/or transport of the treated coal in the container so as to maintain a reduced oxygen content therein.

2. A process as claimed in claim 1 wherein the displacement station has a displacement zone through which the coal in particulate form is passed and wherein the non-oxidizing gas is introduced into the displacement zone to create a counter flow direction of gas 20 movement whereby the non-oxidizing gas displaces and substitutes for a substantial proportion of air within the coal passing through the displacement zone.

3. A process as claimed in claim 2 wherein the parameters of the coal and its flow through the displacement zone and parameters of the introduction and flow of the non oxidizing gas results in substantial fluidization of the particulate coal passing through the 25 displacement zone.

4. A process as claimed in any one of the preceding claims wherein the closeable container is a closeable package, such as a flexible bulk container, which can be handled as a discrete article in its storage and/or transportation.

5. A process as claimed in claim 4 wherein the process includes feeding the treated coal 30 with the reduced oxygen content from the displacement station to a separate packaging station where the at least partial filling of the closeable container occurs.

6. A process as claimed in claim 5 wherein the flow path of the treated coal being fed from the displacement station to the packaging station and the path of the treated coal 10 within the packaging station entering the closeable container is maintained substantially closed so that no substantial quantity of ambient oxygen is reintroduced into the coal to displace non-oxidizing gas therein.

7. A process as claimed in any one of claims 4 to 6 wherein the closeable container is 5 substantially impermeable to gas and wherein the step of closing the container comprises sealing the container so that the resulting sealed container is substantially impermeable to gas.

8. A process as claimed in any one of the preceding claims wherein the step of increasing the packing density comprises compacting and/or settling of the treated coal 10 within the closeable container, the process including the further step of adding more treated coal to the container after the step of compacting and/or settling and thereafter repeating the compacting and/or settling step.

9. A process as claimed in any one of the preceding claims wherein the non-oxidizing gas includes carbon dioxide or nitrogen or treated flue gas or mixtures thereof 15

10 A process as claimed in any one of the preceding claims wherein the oxygen content of the gas mixed with the treated coal emerging from the displacement station is less than about 13% by volume, and most preferably is less than or equal to about 7% by volume.

11, Apparatus for handling of a low-rank coal, such as dried brown coal, for storage and/or transport, the apparatus including: 20 means for feeding a dried low-rank coal with a relatively low water content in a particulate form (which includes in the form of powder, fines, grus, granules, grains, pellets, briquettes and/or blocks) to a displacement means; gas supply means associated with the displacement means and operative to supply a non-oxidizing gas to the fed coal in particulate form in the displacement means so as to 25 displace a substantial proportion of air mixed with the fed coal with the non-oxidizing gas and thereby produce a treated coal having a reduced oxygen content of the gas mixed with the particulates; filling means operative to at least partially fill a closeable container, such as a flexible bulk container, with the treated coal; 30 means for increasing the packing density by compacting/settling the treated coal within the closeable container; and means for closing the container for storage and/or transport of the treated coal in the container so as to maintain a reduced oxygen content therein. I I

12. Apparatus as claimed in claim 11 wherein the displacement means includes a displacement tower through which the particulate coal falls under gravity and wherein the gas supply means comprises multiple gas introduction means distributed in the displacement tower to introduce the non-oxidizing gas generally throughout the flow area 5 of the falling particulate coal.

13. Apparatus as claimed in claim 11 or 12 wherein the closeable container is a closeable package, such as a flexible bulk container, which can be handled as a discrete article in its storage and/or transportation and wherein the filling means comprises a packaging apparatus separate from and downstream of the displacement means and to ia which the treated coal is fed in a closed path inhibiting introduction of oxygen into the flow and to displace non-oxidizing gas,

14. Apparatus as claimed in claim 13 wherein the means to increase the density comprises means for compacting and/or settling treated coal introduced into the container, the apparatus further being operative to introduce more treated coal into the 15 container after the means to increase density has been operated to compact or settle coal within the container, the increase in density and addition of more coal being repeated at least once until a predetermined amount of treated coal has been introduced into the container.

15. Apparatus as claimed in any one of claims 11 to 14 wherein the non-oxidizing gas 20 includes carbon dioxide or nitrogen or treated flue gas or mixtures thereof.

16. Apparatus as claimed in any one of claims 11 to 15 wherein the closeable container, such as a flexible bulk container, is substantially impermeable to gas and wherein the means for closing the container is operative to seal the container so that the resulting sealed container is substantially impermeable to gas. 25

17. Apparatus as claimed in any one of claims 11 to 16 wherein the oxygen content of the gas mixed with the treated coal emerging from the displacement means is less than about 13% by volume, and most preferably is less than or equal to about 7% by volume.

18. Apparatus as claimed in claim 11 and substantially as herein before described with particular reference to the accompanying drawings, 12