Claims: , Description:IMPROVED SYSTEM FOR REAL TIME ONLINE CONTROL AND MONITORING OF RAW MIX BIN LEVEL FOR A SINTERING PLANT

FIELD OF INVENTION

The present invention relates to an improved system for real time online control and monitoring of raw mix bin level and associated technological processes for a sintering plant.

BACKGROUND ART

Sinter is the main raw material for blast furnace. Sintering is a crucial part in iron making process. The natural iron ore occurring in the mines contains impurities like alumina, silicate, phosphorous, sulphur etc. The ores are generally beneficiated to minimise these impurities and enrich iron percentage. However, this beneficiation process creates some fine grains with size less than 10 mm, which cannot be charged directly into Blast Furnaces. This is because it is not possible to charge too many fine materials in Blast Furnace as it would lead to a blockage of flow of the reducing gas. Further, coal also cannot be charged into a blast furnace due to the lack of physical strength required to withstand the conditions inside the furnace. Mainly due to the above reasons, prior to charging in Blast Furnaces, Iron Ores fines are pre-treated for Sinter Formation. The sintering process involves agglomeration i.e. heating of raw mix which primarily consists of iron ore fines, coke breeze, metallurgical wastes, lime, dolomite etc. to produce a semi molten mass that solidifies into porous pieces of sinter with the size and strength characteristics necessary for feeding into the blast furnace. The sintering of iron ore is imperative for improving Blast Furnace productivity, hot metal quality and optimising resource utilization in iron making process.

The Sinter making process comprises of many sub process like, primary mixing of raw materials (iron ore, dolomite, lime, fines etc.) followed by secondary mixing of raw material with water in nodulizing drum, maintaining the level within the desired limits in a raw mix bin also referred to as Raw mix hopper, maintaining the bed height and permeability in the sinter pallets, controlling the temperature in ignition furnace at the desired levels, controlling the speed of sintering machine and straight line coolers to the levels so that the sintering process completes before the material leaves the sintering bed. Besides the overall suction and pressure maintaining the individual wind-box pressure and temperature also needs to be continuously monitored. For tighter control over the process, the monitoring and control of the various process parameters needs to be stringent. This calls for an efficient control system to take care of the control needs. Thus, the sinter making process substantially depends on efficient functioning of series of operations. Due to their complex nature and frequent process fluctuations, a precision automation system is imperative in each of these operations, which is also significant for sinter quality improvement and optimum resource utilization. The application of advanced Controllers coupled with powerful programming tools and Human Machine Interfaces (HMI) is essential for composite operations of sinter making.

Any typical raw mix bin level control in a sinter plant involves individual bunker weigh feeder control, a central controller and associated control loops but the heart of the system is the algorithm which gives consistency and reliability to the control. In general, to the best of knowledge feed rate controls in sinter plants are quite operator dependant and fed manually time to time because the control of feed rates and raw mix bin level is not always straight forward. If any corrections are made in the feed rates to control the variations in the raw mix bin level on account of machine speed variation, it is actually reflected typically after some time depending on the length of the total feeding circuit and distance between the weigh feeders and nodulizing drum and distance between modulizing drum and the raw mix bin. Also the controls depend on many other factors like the amount of material available in each bunker, status of operation of individual weigh feeders and so on. So, a predictive type of control is essential specially when a totally uninterrupted process is desired. Due to these limitations, selection and settings of feed rates from the bunkers is generally manual, based on experience of the operator. The new system however facilitates Automatic Control of raw mix bin level in a sinter plant through improvised closed loop automatic blend mix feed rate control based on specialized algorithms and control architecture comprising of central programmable controller, sensors and instrumentation, actuators, Human Machine Interfaces and various subsystems interconnected through industrial network.

The automation system facilitates a comprehensive control panacea for complete automatic control of raw mix bin level for a constant flow of material in the sinter machine and with consistent quality by also controlling the quantity of water addition in the raw mix through state-of-the-art Programmable Logic Controller (PLC) based process control system. A user’s friendly Human Machine Interface (HMI) has also been developed for centralized monitoring, operation and control of sinter machine as well as for fine tuning of the algorithm. The automation system has resulted in significant improvement in plant performance in terms of productivity and energy savings.

OBJECT OF THE INVENTION
Therefore the principle object of the present invention is to provide system with complete automatic control of raw mix bin level for a constant flow of material in the sinter machine and with consistent quality by also controlling the quantity of water addition in the raw mix. The system also takes care of machine speed variations and automatically adjusts the input feed rate. The system also enables maintaining raw mix bin level even when any weigh feeder is down or any bunker is empty provided the total feed rate of material can be obtained from summing of maximum individual capacity of each running weigh feeder. All this is achieved through general purpose programmable logic controller and a specialized algorithm programmed into it. The new system has several other features also built into it to fine tune the system on-line and to enhance production management.

SUMMARY OF INVENTION

The proposed system for real time online control and monitoring of raw mix bin level and associated technological processes for a sintering plant includes programming and control over the material feeding circuits of a sinter plant typically comprising of a Sinter Mix Bin Building (SMBB), Nodulising Building (NB), Sinter Building, Conveyors, junction house and galleries. In the new system it was also envisaged to provide enhanced monitoring for optimization of sintering process. A typical layout of a sinter plant and sinter machine feeding circuit is given in Fig. 1.

The disclosed system has enabled complete automatic control of raw mix bin level and thus helped in constant flow of material in the sinter machine and with consistent quality by also controlling the quantity of water addition in the raw mix. The new system also takes care of machine speed variations and automatically adjusts the input feed rate. The system also enables maintaining raw mix bin level even when any weigh feeder is down or any bunker is empty provided the total feed rate of material can be obtained from summing of maximum individual capacity of each running weigh feeder.All this is achieved through general purpose programmable logic controller and a specialized algorithm programmed into it. The new system has several other features also built into it to fine tune the system on-line and to enhance production management

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Fig. 1 illustrates typical layout of a sinter plant and sinter machine feeding circuit as prior art.
Fig. 2 illustrates the block diagram of the system hardware in accordance with the present invention;
Fig. 3 illustrates the control schematic in accordance with the present invention;.
Fig. 4 illustrates the control algorithm in accordance with the present invention;
Fig. 5 illustrates the typical values of various set points that enables raw mix bin level control in SP2, DSP in accordance with the present invention;

DETAILED DESCRIPTION

The architecture of automation system has been carefully designed to cater the requirement of cascaded process control loops of Sinter Plant. The overall performance of Sinter Machine depends on accuracy of individual control actions each contributing to sinter quality. To ensure uninterrupted plant operation, PLC is selected with high availability, fault tolerant and dual redundant configuration w. r. t. processor, communication and networking. The field instrumentation is connected with the system through various analog and digital input / output cards. The I/O cards are linked with processors through redundant networks. The operation of Sinter Machine is controlled and monitored from remote location. The processor and operator’s consoles are also connected through redundant Ethernet networks. The PLC system is dovetailed with weigh feeder controllers and other control systems and PLCs of the shop for seamless operation. The schematic of system with process control modules is depicted in Fig. 3.

Raw mix is fed into the nodulizing drum through dedicated weigh feeders. After the water mixing in the nodulizing drum, material falls through conveyors into the raw mix bin also called hopper. The primary control variable in this segment of Sinter Machine is feed rates of weigh feeders, which are controlled through dedicated controller panels. The weight of individual bins, Raw Mix Bin weight, nodulizing drum speed, individual weigh feeder running status, running status of conveyors in the circuit, sinter machine speed are the key process inputs. Based on these inputs the centralized controller operates on the special algorithms programmed in it and generates set points for individual weigh feeder feed rates, thus effecting Raw mix bin level control. Based on actual and set feed rates, the individual controllers in weigh feeder panels generate reference signal for Variable Frequency Drives (VFD), which finally controls the feed rates . The safety and other electrical interlocks are also taken care in all the controllers.

All the weigh feeder control panels, Raw mix bin level control panel and PLC system have been seamlessly integrated for bidirectional communication.. The system also has provision of directly adjusting feed rates of individual feeders, if required. All the important status parameters and control signals are available in HMI for monitoring and control through dynamic visualization graphics in the form of animations, bar graphs, trends etc. The control schematic and the algorithm is shown in Fig. 3 and 4 respectively. The typical values of various set points that enables raw mix bin level control in SP2, DSP is given in Fig. 5.

Inventive step
i. PLC & Remote I/O based redundant automation system with Profibus communication network over Fibre Optic/Cat 6 network and industrial grade networking accessories with application software, digital and analog inputs and outputs for connection of signals pertaining to raw mix bin weights, weights in the bunkers and other required process inputs. Innovative algorithms are used to control the critical raw mix bin level within a desired and predefined range continuously without any operator intervention once the software is initialized. The system implemented at SP2, DSP is based on S7 414H Processor
ii. Remote I/Os for connection of field signals from weigh feeders and plant interlocks.
iii. Weigh feeders with controllers for feeding from the various bunkers.
iv. Load cells for raw mix bin weights
v. Load cells for bunkers weights
vi. HMI terminals for operation and monitoring.
vii. The logic for processing outputs (Control & Indications) are built in the PLC.
viii. The unique algorithm which ensures fool proof control of Raw mix bin level is implemented in the combined architecture of PLC and HMI.
• The automatic raw mix bin feed rate control prevents the level reaching the undesirable upper and lower levels and thus reduces frequent stopping of the critical water addition cum nodulizing process in the mixer drum.
• Maintaining the raw mix bin level in a desired range also facilitates uniform bedding on the sinter bed thereby facilitating uniform sintering process and thus improve the sinter quality.
• The system takes care of machine speed variations also and dynamically adjusts the feed rates to maintain the raw mix bin level. The water addition to the blend mix is also automatically corrected
based on the total feed rate.
• The system also enables maintaining raw mix bin level even when any weigh feeder is down or any bunker is empty provided the total feed rate of material can be obtained from summing of maximum individual capacity of each running weigh feeder.
• User friendly Human machine interface has been designed for on-line display and monitoring of the complete process as well as easy calibration of the raw mix bin level control system without the need to modify the PLC program.

Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. It will be apparent to those having ordinary skill in the art that a number of changes, modifications, variations, or alterations to the invention as described herein may be made, none of which depart from the spirit or scope of the present invention. The particular embodiments and applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, and alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.