WO2008007387A1

WO2008007387A1 - A dust recycling system for enhanced availability of corex

Info

Publication number: WO2008007387A1
Application number: PCT/IN2006/000443
Authority: WO
Inventors: Rajashekhar Pattanasetty; Ramana Venkata Matta; Ramesh Khandre; Shivanagouda
Original assignee: Jsw Steel Limited
Priority date: 2006-07-10
Filing date: 2006-11-08
Publication date: 2008-01-17
Also published as: CN101365810A; KR20090031495A; KR101275107B1; AT505201A2; AT505201B1; ZA200803129B; CN101365810B

Abstract

A dust recycling system to capture dust from reduction gas and inject the same back into the melter gasifier for dust burning in a smelting reduction iron making process comprising a hot gas cyclone (HGC) a dust bin (LDB) in operative connection to said hot gas cyclone for continuous flow of the captured dust through a hot knife gate and valve vertical pipelines provided at an inclination ranging from 40 to 120 preferably 80; said dust bin (LDB) further operatively connected through a vertical pipeline and an inlet to a high dust volume T-piece (TP) comprising of injector and diffuser means; and a melter gasifier having dust burner to burn the dust thus recycled into the melter gasifier through said T-piece. The above system is adapted to favour effective and jam free transportation of dust from the hot gas cyclone to the dust burner and thereby improve plant availability/efficiency.

Description

TITLE: A DUST RECYCLING SYSTEM FOR ENHANCED AVAILABILITY OF COREX. Field of The Invention

The present invention relates to dust recycling system and, in particular, to a dust recycling system to capture dust from reduction gas and inject the same back into the melter gasifier for dust burning in a smelting reduction iron making process.

Importantly, the dust recycling system of the invention is adapted so as to reduce line jamming in dust recycling systems and thereby improve plant availability and efficiency.

The dust recycling system of the invention can thus take high dust loads of upto , 8 t/hour. Moreover, the dust recycling system is further adapted to favour simple and easy maintenance of the system for continuous and jam free transportation of dust from hot gas cyclone to the dust burner in a smelting reduction iron making process.

Background Art

It is well known to carry out the smelting reduction iron making process following the conventionally known Corex process. In particular, such smelting reduction iron making process basically involves two reactors, i) the reduction shaft and ii) the melter gasifier. A highly reducing gas is generated in the melter gasifier due to reactions between oxygen and the iron bearing solid and coal burden. The gas carrying fine particlas of the solid burden in the chamber is fed into the reduction shaft for reducing the iron bearing material into iron after routing it through dust separating cyclones. The dust thus separated is next fed back into melter gasifier through a dust recycling system.

Thus, dust recycling systems are provided to facilitate the capture of the dust out of reduction gas and injecting it back into melter gasifier. The carbon out of the dust is burned by oxygen supplied through the dust burner.

In the existing conventionally used recycling systems the same are basically known to involve a hot gas cyclone, upper dust bin, lower dust bin, dust injection system, T-piece and a dust burner which are all operatively connected through vertical pipes and disk gate valves.

The hot gas cyclone used in such recycling systems basically comprises a device which is used to capture the dust out of reduction gas and send the thus separated dust to an upper dust bin. The upper dustbin is an intermediate bin provided to transport the captured dust from the hot gas cyclone to the lower dustbin. Such upper dustbin is known to include pressurizing system and levelers to detect high and low limits. N₂ is supplied at the lower part to fluidize the dust. The lower dustbin is used to transport the dust from the upper dustbin to the injection system through a T-piece. The dust injection system basically comprises of two valves, I) the ball segment valve to control input and the other II) to control flow rate of N₂.

A vertical pipeline with about 300/200mm. inlet is provided to connect the lower dustbin to the T-piece. The discharge of the pipe to the T-piece is about 200/100 mm. The T- piece consists of the injector and diffuser and is of about 400/300mm. diameter. The dust burner is the unit provided to burn the dust carried by the N₂ with oxygen in the melter gasifier.

Importantly, the down operation i.e. transporting of the dust from hot gas cyclone to the dust injector in such convention dust recycling system is done by adjusting the valves in the system. For such purpose the system is provided with upper disk gate valve, lower disk gate valve, upper pressuring valve and lower pressuring valve. Upper disk gate is opened and the lower disk gate is kept closed to carry the dust from the upper dustbin to the lower dustbin. The disk gates are selectively operated according to the level of each of the dustbins to facilitate the above dust recycling process.

While the above existing system for dust recycling in smelter reduction iron making process is known and made available to the art, such a system is found to have certain limitations and draw backs in as far as desired continuous recycling of the dust without any jamming of the operative pipeline is concerned. In particular, such a system essentially required monitoring the frequency at which the dust was collected in the lower dustbin from the upper dustbin in batches to be finally emptied into the dust burner through the T- piece. Thus during any small instability in the furnace such batch process failed to take the desired dust load. This in turn led to frequent jamming in the dust recycling system pipeline at several points and finally led to plant stoppage / nonavailability.

In particular, studies of such conventional dust recycling systems have revealed that there are several frequent jamming points in the recycling pipeline which included a) in the stuffing box of the upper and lower disk gate valves, b) inlet of T-piece and c) in the upper dust bin and the lower dust bin.

More over, the vertical pipeline connecting the T-piece which had a discharge of 200/100 mm. while its opening at the lower dust bin is about 300-200 mm. led to accumulation of dust and coarse particles at the inlet of the T-piece which in turn also caused frequent jamming. The horizontal line to the dust burner is also found to be subject to jamming especially when there are coarser particles in the dust.

It is also noted that the conventional dust recycling systems also suffer from water leakage from the cooling system of the disc gate valve into the furnace. Moreover, studies have revealed that the refractories in the upper dust bin and lower dust bin get loosened due to thermal shocks in such systems and this in turn also jammed the dust recycling system line at several points.

Objects Of The Invention

It is thus the basic object of the present invention to provide a dust recycling system adapted to capture dust from reduction gas and inject the same back into the melter gasifier for dust burning in a smelting reduction iron making process which would avoid the afore discussed problems and draw backs of the conventional dust recycling systems and favour effective and jam free transportation of dust from the hot gas cyclone to the dust burner and thereby improve plant availability/efficiency.

Another object of the present invention is directed to a dust recycling system for recycling the captured dust from the reduction gas and inject into the melter gasifier which would be simple and user friendly and would not require complex and labour intensive monitoring such as for batch transportation of the dust to the dust burner of the conventional art.

Yet another object of the present invention is directed to a dust recycling system for recycling the captured dust from the reduction gas and injecting the gas into the melter gasifier which would be stable and favour continuous transportation of the dust and avoid complexities and problems of batch process due to instabilities in the furnace and the like.

Yet another object of the present invention is directed to dust recycle system to capture dust from reduction gas and inject into the melter gasifier which would avoid problems of frequent jamming in the dust recycling system pipeline and avoid plant stoppage favouring enhanced plant availability and efficiency.

A further object of the present invention is directed to dust recycle system to capture dust from the reduction gas and inject into the melter gasifier which would not have problems of frequent jamming especially in lines such as the stuffing box of upper and lower, gate valves, inlet of T-piece and also in the upper dust bin and lower dust bin as experienced in the conventional dust recycling systems presently in use.

A further object of the present invention is directed to a dust recycling system adapted to capture dust from reduction gas and inject the same into the melter gasifier for dust burning in a smelting reduction iron making process which would avoid accumulation of dust and coarse particles at the inlet of the T-piece and,_, therefore, also avoid frequent jamming in said inlet of the T-piece.

A further object of the present invention is directed to a dust recycling system to capture dust from reduction gas and inject the same back into the melter gasifier wherein the horizontal line of the dust burner would be free of jamming even in case of coarser particles in the dust.

A further object of the present invention is directed to a dust recycle system to capture dust from reduction gas and inject the same into melter gasifier in the dust burning which would avoid any problems of water leakage from cooling system of disk gate valve into the furnace such as in case of the conventional dust recycling systems presently in use.

A further object of the present invention is directed to a dust recycling system to capture dust from reduction gas and inject the same back into the melter gasifier for dust burning in a smelter reduction iron making process which would not encounter problems of loosening of refractories in the upper dust bin and lower dust bin due to thermal shock and consequential jamming of the dust recycling system as experienced under the presently available dust recycling system.

A further object of the present invention is directed to a dust recycling system to capture dust from reduction gas and inject the same back into the melter gasifier for dust burning in a smelter reduction iron making process which would avoid frequent plant stoppage due to blockage of dust recycling system line and also not create back pressure to cyclone as experienced in the presently available system of dust recycling in smelting reduction iron making processes and thereby improve the plant availability and efficiency. Summary Of The Invention

Thus according to the basic aspect of the present invention there is provided a dust recycling system to capture dust from reduction gas and inject the same back into the melter gasifier for dust burning in a smelting reduction iron making process comprising:

a hot gas cyclone adapted to capture the dust out of the reduction gas ;

a dust bin in operative connection to said hot gas cyclone for continuous flow of the captured dust through a hot knife gate and valve vertical pipelines provided at an inclination ranging from 4° to 12° preferably 8° ;

said dust bin further operatively connected through a vertical pipeline and an inlet to a high dust volume T-piece comprising of injector and diffuser means; and

a melter gasifier having dust burner to burn the dust thus recycled into the melter gasifier through said T-piece.

The above disclosed dust recycling system is adapted to transport the dust from hot gas cyclone to the dust burner without jamming of the transport line. Importantly, in the dust recycling system of the invention, the conventional provision of the upper disc gate in such recycling system has been replaced selectively with the bonnet hot knife gate valve, which is preferably obtained of stainless steel. The hot gate knife valve does not require water cooling system and simply requires N₂ cooling system. As would be apparent from the above basic aspect of the dust recycling system of the invention the same has been provided such as to facilitate the process of dust recycling continuous by way of elimination of the upper dust bin completely. For such purpose in the system of the invention the hot gas cyclone is directly operatively connected to lower dust bin using the hot knife gate valve and vertical pipe line having a selective inclination in the range to 4-12° preferably 8°. Such an arrangement also advantageously takes care of the problem of refractories from the upper dustbin jamming at the inlet of T-piece experienced in the presently known dust recycling systems.

According to another aspect of the invention there is provided a dust recycling system to capture dust from reduction gas and inject the same back into the melter gasifier for dust burning in a smelting reduction iron making process comprising: a hot gas cyclone adapted to capture the dust out of the reduction gas ;

said dust bin further operatively connected through a vertical pipeline and an inlet to a high dust volume T-piece comprising of injector and diffuser means;

a melter gasifier having dust burner to burn the dust thus recycled into the melter gasifier through said T-piece; and

a catch pot adapted to collect the dust or coarser particles for online cleaning and elimination of line jamming.

Accordingly to the above further aspect of the dust recycling system of the . invention to favour collection of dust or coarser particles during any suspects, a catch pot below the dust recycling system line has been provided in the system of the present invention. Such catch pot and its provision is directed to facilitate the online cleaning of the dust recycling system line and complete elimination of dust recycling system line jamming.

According to another aspect of the invention there is provided a dust recycling system to capture dust from reduction gas and inject the same back into the melter gasifier for dust burning in a smelting reduction iron making process comprising:

a hot gas cyclone adapted to capture the dust out of the reduction gas ;

a melter gasifier having dust burner to burn the dust thus recycled into the melter gasifier through said T-piece; a catch pot adapted to collect the dust or coarser particles for online cleaning and elimination of line jamming; and

a manhole for easy maintenance and cleaning.

The above provision of the manhole in the system is further directed to favour easy maintenance and cleaning of the system.

Importantly in the above dust recycling system the bonnet hot knife gate valve is selectively obtained of Stainless Steel. Also, the bonnet hot knife gate valve comprises N₂ cooling system. In the above system of the invention the vertical pipe-line is operatively connecting the T-piece through an inlet of 300/200 mm inline with the vertical pipe. The said T-piece to accommodate high dust volumes comprises T-piece of 500/400 mm.

In accordance with another preferred aspect of the invention the dust recycling system includes a grid means there between the injector and diffuser such as to screen out lump pieces and avoid jamming of horizontal line to dust burners.

It would be apparent from the above that the present dust recycling system of this invention is simple to obtain and also due to continuous and jam free transportation of the dust from the hot gas cyclone to the dust burner it is possible to avoid plant down time and provide for this improved availability and efficiency with simple and effective cleaning and maintenance facilities. Further the system also favours taking high dust loads of even upto about 8t/hour.

Brief Description Of The Accompanying Figures:

The details of the invention, its objects and advantages are explained hereunder in greater detail in relation to non-limiting exemplary illustrations as per the following accompanying figures wherein:

Figure 1 : illustrates a conventional dust recycling system line used in smelting reduction iron making process; and

Figure 2 : illustrates an embodiment of the dust recycling system line in accordance with the present invention for use in smelting reduction iron making process. Reference is first invited to accompanying figure 1 which illustrates the conventional dust recycling system line presently available and provided to capture dust out of reduction gas and to inject it back into melter - gasifier.

As illustrate in figure 1 the presently available and existing dust recycling system line basically comprises of the hot gas cyclone (HGC), upper dust bin (UDB), lower dust bin (LDB), dust injection system, T-piece (TP) and dust burner . All the above operative constituents of the dust recycling system are operatively connect through vertical pipes and disk gate valves as further illustrated in the figure.

As clearly apparent from figure 1, in such existing dust recycling system lines, in the hot gas cyclone (HGC) the dust from the reduction gas is captured and the separated dust is sent to the upper dustbin (UDB). In particular, the UDB is an intermediate bin i.e. provided to transport the captured dust from cyclone to the lower dustbin (LDB). The upper dustbin (UDB) is comprised of pressurizing system and levelers to detect high and low limit. The N₂ is supplied at lower part to fluidize the dust.

The lower dustbin (LDB) in the conventional system is used to transport the dust from the upper dustbin (UDB) to injection system through a T-piece (TP). The dust injection system is basically comprised of two valves, one is the ball segment valve to control the input and other is to control flow rate of N₂.

A vertical pipeline with 300/200mm. inlet connects lower dust bin (LDB) to T-piece. The discharge of the pipe to T-piece is 200/100 mm. The T-piece comprises of the injector and the diffuser as also shown in the figure. The T-piece is usually provided with 400/300mm. dia.

The dust thus captured is burnt in the dust burner which is an equipment provided to burn the dust carried by N₂ with oxygen in the melter gasifier.

As would be apparent from the above existing dust recycling system line, the down operation i.e. the transporting of the dust from the hot gas cyclone (HGC) to the dust injector is carried out by adjusting the valves in the system. For such purpose the system is provided with upper disk gate valve, lower disk gate valve, upper pressurizing valve and lower pressurizing valve. The upper disk gate is opened and lower disk gate is kept closed to carry the dust from the upper dustbin (UDB) to the lower dustbin (LDB). The disk gates are operated according to the levels of each dustbin. Thus in such existing dust recycling system the dust collected in the lower dust bin (LDB) from the upper dust bin is in batches which get emptied into the dust burner through T- piece at designed frequency. Thus, in case of small instability in the furnace such batch process is unable to take the dust load. This led to frequent jamming in the dust recycling system line at several points and finally to plant stoppage. In particular, the frequent jamming points in the line were identified to include a) in the stuffing box of upper and lower disk gate (LDG) valves, b) inlet of T-piece and c) in the upper dust bin (UDB) and the lower dust bin (LDB).

Moreover, in the existing system the vertical pipeline connecting the T-piece is provided with the discharge of 200/lOOmm. while its opening in LDB is 300/200mm. This led to accumulation of dust and coarse particles at the inlet of T-piece resulting in frequent jamming.

Also the horizontal line to dust burners in such convention system also was subject to jamming in case of coarser particle in the dust. Water leakage from cooling system of disk gate valve into the furnace is also experienced. Moreover, in such conventional systems, the refractory in the upper dust bin (UDB) and the lower dust bin (LDB) are found to get loosened due to thermal shocks leading to further jamming of the dust recycling system line at several points.

Reference is now invited to accompanying figure 2 which illustrates the dust recycling system line for smelting reduction iron making process as provided in accordance with the present invention to favour reduction in dust recycling system line jamming and thereby improve the plant availability.

As clearly illustrated in figure 2 the dust recycling system line of the present invention is adapted to transport the dust from the hot gas cyclone (HGC) to the dust burner continuously without jamming the line. This is achieved by way of selective provision of the dust recycling system as illustrated in figure 2.

In particular, as apparent from figure 2, the dust recycling system of the invention, the upper disk gate (UDG) valve of the existing system of figure 1 has been avoided in the present system of the invention with the provision of the bonnet hot line gate valve (KGV) preferably obtained of stainless steel. The hot gate knife valve (KGV) provided in the system of the invention does not require water cooling system but simply requires N₂ cooling system. Moreover, the dust recycling system of the invention of figure 2 has been advantageously made continuous by eliminating the requirement of any upper dustbin (UDB) used in the conventional system of Figure 1 discussed above. Thus, in the present system the hot gas cyclone (HGC) is operatively connected directly to the lower dust bin (LDB) involving selectively the hot knife gate valve and vertical pipe line at an inclination ranging from 4-12° preferably 8°. This also favours eliminating the problem of jamming due to refractories from the UDB jamming at the inlet of the T-piece.

Also, the lower disk gate valve used in the conventional system of Figure 1 was found not required in the continuous system of dust transportation in accordance with the invention as shown in figure 2. Accordingly, in the present system the lower disk gate valve has been completely eliminated.

The vertical pipeline connecting the T-piece with an inlet, which was under the conventional system of the Figure 1 of 200/100mm has been selectively changed by provision of 300/200mm. in line with the vertical pipe to favour effective transport of the dust. Also, the T-piece, which was under the conventional art of 400-300mm. has been selectively changed in the present system to preferably 500/400 mm. to favour accommodating high dust volume. A grid means has been further introduced in the present dust recycling system in between the injector and the diffuser so as to screen out lump pieces and avoid jamming of horizontal line to dust burner. A manhole has been introduced in the system to further facilitate easy maintenance and cleaning of the dust recycling system.

In accordance with the further aspect of the invention in the present dust recycling system in order to favour collection of the dust of coarser particles during any suspect, a catch pot (CP) below the dust recycling system line has been provided. This facilitates online cleaning of the dust recycling system line and complete elimination of the dust recycling system line jamming.

The advantages by way of reduced dust recycling line jamming using the system of the invention as per figure 2 vis-a-vis the existing system (figure 1) was further studied and the number of times the DRS lines jammed during the year noted under several trials when using the existing system and that encountered when using the present system were noted and results are reproduced hereunder in Table 1: Table - 1

As apparent in Table 1 the total number of times the dust recycling system line jam during several yearly trials substantially reduced in use of the dust recycling system of the present invention.

Also further studies were carried out to ascertain the number of yearly unplanned shut downs required due to line jamming when using the existing DRS (figure 1) vis-a-vis due to the DRS of the present invention (figure 2) and the results of such trials are provided hereunder in Table 2:

Table 2

The above results in Table 2 further confirm that the present dust recycling system line of the invention resulted in 100% availability of plant and no unplanned shut down were required using the present dust recycling system of the invention. Importantly, the online cleaning facility in the present DRS line of the invention has completed eliminated the problems of shut down resulting from DRS line jamming.

Advantageously, therefore, the present dust recycling system of the invention favours achieving 100% availability of plant with substantial reduction of line jamming which can also be cleaned on line using the catch pot of the present system. Moreover, the present system being a continuous mode of transport of dust from the hot gas cyclone to the dust burner without jamming of line is adapted to take high dust load than the existing dust recycling system to favour effective and advantageously application and use of such dust recycling system in smelting reduction iron making processes.

Claims

We Claim:

1. A dust recycling system to capture dust from reduction gas and inject the same back into the melter gasifier for dust burning for use in a smelting reduction iron making process comprising:

a hot gas cyclone adapted to capture the dust out of the reduction gas ;

2. A dust recycling system to capture dust from reduction gas and inject the same back into the melter gasifier for dust burning for use in a smelting reduction iron making process comprising:

a hot gas cyclone adapted to capture the dust out of the reduction gas ;

3. A dust recycling system to capture dust from reduction gas and inject the same back into the melter gasifier for dust burning for use in a smelting reduction iron making process comprising:

a hot gas cyclone adapted to capture the dust out of the reduction gas ;

a melter gasifier having dust burner to burn the dust thus recycled into the melter gasifier through said T-piece;

a catch pot adapted to collect the dust or coarser particles for online cleaning and elimination of line jamming; and

a manhole for easy maintenance and cleaning.

4. A dust recycling system as claimed in anyone of claims 1 to 3 wherein the bonnet hot knife gate valve is selectively obtained of Stainless Steel.

5. A dust recycling system as claimed in anyone of claims 1 to 4 wherein the bonnet hot knife gate valve comprises N₂ cooling system.

6. A dust recycling system as claimed in anyone of claims 1 to 5 wherein the vertical pipeline is operatively connecting the T-piece through an inlet of 300/200 mm inline with the vertical pipe.

7. A dust recycling system as claimed in anyone of claims 1 to 6 wherein the said T- piece to accommodate high dust volumes comprises T-piece of 500/400 mm.

8. A dust recycling system as claimed in anyone of claims 1 to 7 comprising a grid means there between the injector and diffuser such as to screen out lump pieces and avoid jamming of horizontal line to dust burners.

9. A dust recycling system as claimed in anyone of claims 1 to 7 adapted to take dust loads upto 8t/hr.

10. A dust recycling system to capture dust from reduction gas and inject the same back into the melter gasifier for dust burning for use in a smelting reduction iron making process substantially as herein described and illustrated with reference to the accompanying figure 2.