Title of Invention

"A DEVICE FOR MAINTAINING FURNACE HEAT ABSORPTION OPTIMALLY FOR COAL FIRED BOILERS."

Abstract

A device for maintaining furnace heat absorption optimally for coal fired boilers comprising super heater sprayer (1), signal conditioner <2), a logic panel <3), a man machine interface system (4), a motor control centre (5) and a wall blower local control system <6), said supef heater sprayer being located at the top of the boiler furnace and connected to said signal conditioner, said logic signal being connected to said signal conditioner and said motor control centre, said Man Machine Interface being actuated by said logic panel to operate the wall blowing system for blowing hot air into the furnace through wall blower local control.

Full Text

FIELD AND BACKGROUND OF THE INVENTION The present invention relates to a device for maintaining furnace heat absorption optimally for coal fired boilers. The present invention particularly relates to wall blowing in pulverized coal fired boilers which would operate need based, automatically starting and stopping the wall blowing system to maintain the furnace water wall heat absorption within optimum range. •The radiation and convection zone heat transfer surfaces of a boiler are designed to absorb proportionately the heat released on combustion of fuel (Coal) such that various functions such as water preheating (economizer), steam generation (water wall), steam super heating (LTSH, Platent SH and Final SH), steam reheating and air heating are carried out optimally. The boiler furnace, where the fuel is burnt, absorbs the maximum of the heat released. Impurities, if present, in the fuels cause deposits on boiler water wall srfaces resulting inthe reduction of furnace heat absorption. The pattern, nature and rate of deposition vary along various zones of the furnace. Due to the combined effects of differing heat release rates of fuels and varying depositions on water walls and further depending on boiler load, mill combinations, tilt etc, the net furnace heat absorption could vary dynamically from the design value. If the furnace heat absorption is lowered, the furnace outlet gas temperatures go up resulting in increased SH/RH sprays, increased metal temperatures as well as increased NOx levels due to higher furnace temperatures. The cycle efficiency of power plant suffers on increases in sprays, viz. with increase in re-heater spray in 210 MW designs and with increase in both SH/RH sprays in 500 MW designs. On the other hand, if furnace heat absorption increases, the furnace outlet gas temperature and SH/RH steam temperatures fall short of design value resulting in lower efficiency. Due to fluctuating fuel characteristics, most of the boilers in India experience varying degrees of sprays or low steam temperature conditions. Hence, maintaining furnace heat absorption optimally is a key operational requirement to maintain efficient boiler performance. CONVENTIONAL WALL BLOWING SYSTEMS In boilers, wall blowers are located at different elevations above and below the burner zones on all the four walls for removing deposits. As such all the wall blowers are normally operated once in a shift, sequenced one after the other. That is, approximately 3 times a day all wall blowers are operated. The conventional wall blowing system has certain disadvantages viz. being routine and ritualistic in nature, does not recognize and differentiate whether the furnace is absorbing heat optimally or in other words whether it is absorbing less or more than the optimum value and once started, it resorts to wall blowing from the first to the last of wall blower. If the furnace deposition had been less, the excess furnace cleaning might result in higher furnace heat absorption and lesser Super heat temperatures. Many a times the benefit of better heat absorption and lesseer spray could be only for a shorter period with lesser heat absorption and higher spray for the rest of the period till the next wall blowing. Japan Patent No.JP 62009113A2 illustrates controlling the operation of the Soort Blowers by image data obtained by a pick up cameras provided to scan respective pre determined areas of the furnace. Plurality of images obtained from TV cameras pickup state of the dust accumulated on the water walls and optical images are converted into electricals signal which is further converted to digital signals and stored in image processing arithmetic unit. The image data, tube edge pattern and condition of the unit are processed by a dust thickness processing program. A temperature controlling device takes these data and decides the soot blower controlling signals based on programmed factors. Japan Patent No.JP 62017512A2 illustrates a method of group operation of soot blowers for effective removal of adhered substances based on a coat starting pattern derived from coal properties and the read operational pattern. Japan Patent No.JP 11148633A2 illustrates a method by which based on differential between calculated and reference furnace outlet temperature the starting order of soot blowing is corrected automatically. Assuming the reference coal is an intermediate fuel coal, the gas temperature difference increases on the plus side for high fuel ratio (Fixed carbon to volatile matter ratio in proximate analysis of coals) and on the minus side for low fuel ratio of coals. Hence the prior art does not contain a teaching that the super heater spray level signals can be utilized for selecting high & low set points which in turn can atomatically start & stop the Soot/wall blowers. It is an object of the present invention to mitigate the above drawbacks of the conventional devices for maintenance of the furnace heat absorption. A further object of the present invention is to maintain furnace water wall heat absorption at an optimum range by activating the operation and stopping of the wall blowers by preselected signals. SUMMARY OF THE INVENTION The device developed by the applicant maintains the furnace water wall heat absorption at optimum levels by operating the preprogrammed set of wall blowers activated by the signals such as Super heater spray exceeding "High" set points and permissive such as soot blowing header steam temperature, etc. and by discontinuing operation of next wall blower when Sper heater spray level reduces below the low set point, so that referred boiler parameter variations are minimized and the overall boiler performance is improved. In this system wall blowers are operated one wall after another wall in staggered manner but in sequence as demanded by the system. The fundamental concept behind the need for the present invention is that - 1. There is a requirement of a system, in addition to the generally existing burner tilting arrangement of tangential firing system, which would operate need based, to maintain the furnace heat absorption optimally so that neither Super heater steam temperature falls short nor go up resulting in higher Super heater spray which would take cognizence of the variations in net furnace heat absorption due to changes in coal quality, boiler load, mill combinations, burner tilt, etc. 2. There is need to reduce the frequency of wall blowing to minimize the erosion of water wall tubes due to steam blowing. 3. There is a need to reduce the SH/RH sprays and there by improve the cycle efficiency or in other words reduce the heat rate of the power plant to the extent possible by operational means as well as reduce the Demineralised (DM) water otherwise wasted as spray and the associated energy needed to convert water to steam. 4. There is a need to prevent excursions of convection pass heat transfer surface metal temperatures above the permissible limit, there by retaining the respective designed creep life of metals. 5. There is need for a system which would cognize dynamically and operate automatically. DESCRIPTION OF THE ACCOMPANYING DRAWINGS The improved device for maintaining furnace heat absorption for coal fired boiler of the present invention is described hereinbelow with reference to the accompanying drawings. In the drawings - Fig.l shows block diagram showing the various sub systems where in the Super heater spray flow measured (1) is signal conditioned (2) and fed to a logic panel (3) for signal processing. The logic panel interacts with a personal computer based Man Machine Interface (MMI) system (4) and decides actuating the wall blower (WB) through a Motor Control Center (MCC) (5) and wall blower local control (6). Fig.2 shows a flow chart of the logics implemented in the logic panel. As the Super heater Spray Flow (SHSF) goes up if the furnace heat absorption is reduced due to deposition, SHSF measurement is taken as a monitoring signal for either starting the wall blowing or for stopping the wall blower. When the SHSF exceeds high set point, the logic decides to activate the wall blowing cycle in the sequence from where it was left. Actual wall blowing is started after ensuring permissives such as minimum steam temperature and steam pressure. The wall blowing is carried in increments of group of blowers. The SHSF is checked and compared with set point on completion of every group of wall blowing. When SHSF reaches below low set point, the wall blowing sequence is halted and waits for the SHSF to exceed set value for activating/starting the sequence again. This logic system is designed to respond appropriately to varying operational/performance conditions such as SHSF being continuously HIGH or LOW or when it is between the LOWER and HIGHER set points. Whenever SHSF measurement is continuously greater than set point, even after completing one cycle of wall blowing sequence, the logic changes over to operator interactive mode after giving an alarm, over which the operator can either decide to continue or change set point. Whenever SHSF measurement is continuously lower than set point for a preset period, the logic changes over to operator interactive mode after giving an alarm, over which the operator can either decide to continue or change set point. Whenever SHSF measurement is continuously lower than the high set point and greater than the low set point for a preset period, the logic activates a group of wall blowers from where it was left previously. Whenever the fault occurs due to wall blowing steam parameters or the wall blower stuck up conditions, the system alarms and switches over to operator intervention mode to clear the faults. After the fault clearance, the operator can switch over to auto mode, where the system continues from where it was left. Similarly the auto operation of the system can be manually/ automatically put on hold to facilitate operating blowers other than the boiler furnace such as Long Range Soot Blowers (LRSB) in the convection pass of the boiler or Air Preheater blowers and resume back to furnace wall blowing from where it was left previously. The Man Machine Interface (MMI) deployed in this system in built with operator friendly displays through a personal Computer. The system displays, the mimic of wall blower arrangement, Soot blowing steam header valve open or close, drain temperature, steam temperature and pressure, Super heater/Re-heater spray flows, boiler main flow, blower status such as home position, forward, retract, alarm status of wall blowing system, the status of timers built in the claimed logics and Super heater high & low set points. The system installed can minimize the operator intervention, average Super heater/Re-heater sprays and the number of cycles of wall blowing significantly. The various features of novelty which characterize the invention are pointed out, with particlarly, the claims annexed to and forming the part of the disclosure. For a better understanding of the invention, its operating advantages and specific results attained by its users, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. WE CLAIM! .1. . A device for maintaining furnace heat absorption optimally for coal fired boilers comprising super heater sprayer , signal conditioner , a logic panel (3), a man machine interface system 2. A device for maintaining furnace heat absorption optimally for coal fired boilers as clailmed in Claim 1, said furnace is provided with a super heater. 3. A device as claimed in Claim 1 or 2 which maintains the furnace heat absorption at optimum levels by operating wall blowers as per certain preprogrammed logics activated by the Super heater spray flow, high and low set points, soot blowing header steam pressure and temperature, response time so that furnace gas outlet and average Super heater/Re-heater sprays are reduced and the overall boiler performance is improved. 4. A device as claimed in Claim 3 wherein said device is provided with mechanical, electrical and electronic hardware and software with data acquisition and display, which can be incorporated as a system in all new soot blowing installation and also as an add-on system to existing soot/wall blowing with much operational flexibility. 5. A device as claimed in Claim 3 or 4 wherein said logics are built in the personal computer/programmable logic controller. 6. A device as claimed in Claims 3 to 5 wherein said aoot blowing steam header valve gets closed automatically once th» SHSF reaches below the low set point. 7. A device as claimed in any of the preceding claims wherein the Man Machine Interface is built with operator friendly displays through a personal computer? the system displays, the mimic of wall blower arrangement, soot blowing steam header valve, drain temperature, steam temperature and pressure, Super heater/Re-heater spray flows, boiler main steam flow, blower status such as home position, forward, retract, alarm status of wall blowing system, the status of timers built as per logics and Super heater high and low set points. 8. A device as claimed in Claim 7 wherein the improved system, the software has inbuilt provisions to alarm and call for operator Intervention only under abnormal situations. 9. A device as claimed in the preceding claims comprising for real time trending of Super heater/Re-heater spray levels, metal temperatures of selected Super heater or Re-heater coils. 10. A device as claimed in Claims 3 to 9 wherein said data acquisition system facilitates survey of data such as cumulative Super heater/Reheater spray levels, as well as furnace outlet temperatures, metal temperatures of selected convection pass heat transfer coils etc. 11. A device as claimed in Claims 3 to 10 wherein said software is provided with means for facilitating switching over to operation of Long Retractable Soot Blowers (LRSBs) in the boiler furnace, as well as air preheater blowers whenever necessary and return back thereafter.

Documents:

451-del-2001-abstract.pdf

451-del-2001-claims.pdf

451-DEL-2001-Correspondence-Others-(05-05-2010).pdf

451-del-2001-correspondence-others.pdf

451-del-2001-correspondence-po.pdf

451-del-2001-description (complete).pdf

451-del-2001-drawings.pdf

451-del-2001-form-1.pdf

451-DEL-2001-Form-15-(05-05-2010).pdf

451-del-2001-form-19.pdf

451-del-2001-form-2.pdf

451-del-2001-form-3.pdf

451-del-2001-form-4.pdf

451-del-2001-form-5.pdf

451-del-2001-gpa.pdf