Title of Invention

AN IMPROVED FUEL-OIL PRESSURE CONTROL SYSTEM FOR AUTO CHANGEOVER OF A GAS TURBINE BETWEEN MAIN FUEL TO STANDBY FUEL OIL MODE

Abstract

Many Gas Turbine plants operate ON "main fuel oil" as well as "standby fuel oil" to ensure uninterrupted operation. In order to ensure uninterrupted operation of Gas Turbine, due to any problem in the operating fuel oil supply system, it should Be possible for the Gas Turbine to change over to the standby fuel oil system, without interruption in the power generation. It has been observed that present fuel oil pressure control systems with conventional PID controllers are not able to sustain the fuel oil pressure during fuel change over conditions, leading to the trip of the Gas Turbine. A suitable control system has been developed and programmed in DCS system for Fuel oil pressure control system for auto change over from "main fuel oil" to "standby fuel oil" And vice versa of Gas Turbine on load.

Full Text

2 FIELD OF INVENTION The invention relates to fuel oil pressure control system of a gas turbine and automatic change over of fuel injection from main fuel oil to stand by fuel oil and vice versa during on load condition. BACKGROUND OF THE INVENTION Gas turbines play a major role as prime movers for many applications including power generation. Fuels play a critical role in power production. The cost and availability of fuel are major planning considerations. Consequently, the ability of any prime mover to bum a wide range of fuels - or fuel flexibility continues to be of primary importance. 3 A Gas Turbine has the capability to operate on more than one fuel. Accordingly, many Gas Turbines are designed to operate on various gaseous as well as liquid fuels to meet the objective of fuel flexibility. In locations, where gas fuel is not readily available, customers will opt operating Gas Turbines on liquid fuels. This Invention pertains to Gas Turbines operating on liquid fuels. Most of the process plants depend on the power generated by the captive Gas Turbine Power Plants. Any Interruption in the power generation will upset the operation of the process plant, leading to heavy economic losses. Hence, there Is a need for standby fuel to ensure uninterrupted process plant operation. Accordingly present Invention alms at development of a method so that Gas Turbine plants operate on "main fuel oil* as well as "standby fuel oil to ensure uninterrupted operation. 4 OBJECTS OF THE INVENTION - the object of the invention is to develop an automatic device to control the fuel oil pressure of main and standby fuel injection system simultaneously for a gas turbine plant on load condition. - other object of the invention Is to develop a means of automatic change over from main fuel oil to standby fuel oil supply system and vice versa during on load condition. - Another object of the invention Is to ensure uninterrupted process of the operation of gas turbine plant preventing loss of production. - Further object of the invention is to provide a means of fuel flexibility for two different fuel oils on the same turbine. 5 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Fif.1. Illustrates: Flow diagram of fuel oil supply system of a typical Gas Turbines Plant, operating on "main fuel oil" as well as "standby fuel oil" [with Conventional PID Pressure Control System] Both the main as well as standby fuel oils are fed by separate fuel forwarding systems up to the three-way valve (12) at the inlet of Gas Turbine. The three-way valve will admit either of the fuel oils into the Gas Turbine at a time, based on the fuel oil selected in the Gas Turbine control system. Typical Fuel forwarding system of each of the fuel oil, basically consists of fuel oil storage tank (1), Duplex strainers (2) fuel oil forwarding pumps (3), fuel oil pressure control value (4), fuel oil fine filters (5) fuel oil flow meters (6), and fuel oil re-circulation lines (10) as indicated In the flow diagram. 6 - storage tank ensures availability of the fuel oil for a given period of time. - the fuel oil forwarding pumps will pump the fuel oil into the Gas Turbine at the required pressure. - The fuel oil filtration system ensures the required cleanliness of oil by the Gas Turbine. - The fuel oil flow meter measures the fuel oil being consumed by Gas Turbine. - The fuel oil pressure control valve maintains the fuel oil pressure at the inlet of Gas Turbine, within the required limits, at all conditions taking Into consideration of various factors such as: (i) variations in pressure drops in the components of fuel oil forwarding system at various fuel oil flows, based on the operating load of the Gas Turbine. 7 (ii) density variations of fuel oil, (iii) variations in oil level in the storage tank, (iv) clogging conditions of fuel oil filters etc. - The fuel oil re-circulation line re-circulates a minimum amount of fuel oil back to the storage tank to enable to the pressure control valve to maintain the required pressure, especially while the fuel stream is In standby mode. The controls directly pertaining to the Gas Turbine proper are implemented through the dedicated control system of the Gas Turbine [Gas Turbine Control System] (15). The controls of the of the balance of the power plant Including controls of the fuel oil forwarding systems for the Gas Turbines are normally operated through DCS system [Distributed Control System] (8). 8 The Gas Turbine requires liquid fuel at a specified minimum pressure at inlet flange of the turbine. Fuel oil pressure, lower than the minimum specified at the inlet of Gas Turbine, can lead to the damage of the Gas Turbine fuel oil system components. Gas Turbine control system will trip the Gas Turbine, in case the fuel oil supply pressure falls below the minimum specified, sensed by pressure switch low-low, PSLL (16) at the inlet of the Gas Turbine. Pressure Transmitter (7) is provided downstream of the pressure control valve (4) of each of the fuel oil forwarding system. Based on the feed back from the pressure signal from the respective pressure transmitters, the pressure control valves maintain the required pressure at the inlet of Gas Turbine, as per the control valve opening signal received from controller in the DCS. Conventionally PID controllers are used as the pressure control valve controllers in the DCS system (8). 9 Whenever the Gas Turbine is operating on "main fuel oil", the "standby fuel oil" pumping system is normally kept in operation. Similarly, whenever the Gas Turbine is operating on "standby fuel oil", the "main fuel oil" pumping system is normally kept in operation. Thus facilitates automatic change over of Gas Turbine to the other fuel, in case of problem in the operating fuel system, thus ensuring uninterrupted operation of the Gas Turbine plant The problem in the operating fuel oil system Is sensed by the pressure switch low, PSL (11) mounted in the respective fuel oil forwarding system. In order to ensure uninterrupted operation of Gas Turbine, If there Is any problem in the "main fuel oil" forwarding system, it should be possible for the Gas Turbine to automatically change over to the "standby fuel oil" supply system, and vice versa, without tripping of the Gas Turbine. When Gas Turbine is operating at load on "main fuel oil", under these conditions, the pressure control valve in the "main fuel oil" forwarding system will be at corresponding higher opening condition. 10 At the same time, pressure control valve in the "standby fuel oil" forwarding system will be in the partially open condition, as there is no flow of this fuel oil into the Gas Turbine, and only recirculatlon flow Is taking place. Any malfunction in the "main fuel oil" forwarding system as detected by Low Pressure Switch, PSL in the "main fuel oil" forwarding system, is sensed by the Gas Turbine control system. Gas Turbine control system gives command to 3-way valve (12) to divert its position from "main fuel oil" to "standby fuel oil", to enable auto change over of Gas Turbine from "main fuel oil mode" to "standby fuel oil mode". At this instant, the opening of the pressure control valve in the "standby fuel oil' system, shall increase to the required higher opening condition automatically from the partially open condition, quickly. Otherwise, the pressure of the fuel oil at the Inlet of Gas Turbine will fall drastically leading to the trip of the Gas Turbine 11 Following are the sequence of events observed, during auto change over of Gas Turbine on load from "main fuel oil" to standby fuel oil with conventional PID control system. 1. Gas Turbine is operating on main fuel oil". 2. Pumping system of "standby fuel oil" is in running condition. 3. Pressure control valve in the "main fuel oil" forwarding system is in the required high open condition based on the command from the PID controller. 4. Pressure control valve In the standby fuel oil" forwarding system is in the partially open condition. 5. Malfunction of the "main fuel oil forwarding system is detected by low pressure switch, PSL in the "main fuel oil." forwarding system. 6. Gas Turbine control system gives command to 3-way valve to divert its position from "main fuel oil" to standby fuel oil, to enable 12 auto change over of Gas Turbine from "main fuel oil mode" to "standby fuel oil mode". 7. Pressure control valve in the standby fuel oil forwarding system is not able to open quickly to the required level. 8. Gas Turbine is tripped on fuel oil pressure low-low at Inlet of Gas Turbine. Therefore (i) The response time of the pressure control valves have no limitations for quick opening application. (ii) The PID controllers are capable of maintaining the required fuel oil pressure during normal operation of the Gas Turbine. However, PID controllers alone are not capable for enabling auto change over of Gas Turbine from one fuel oil to other fuel oil. 13 Hence, there is a need for a fuel oil pressure control system which also ensures auto change over of Gas Turbine from "main fuel oil' to "standby fuel oil" and vice versa. Fig-2 illustrates a schematic diagram of developed fuel oil pressure control system enabling auto change over of Gas Turbine from "main fuel oil" to "standby fuel oil" and vice versa. In order to ensure auto change over of Gas Turbine, from "main fuel oil" to "standby fuel oil" and vice versa, with out tripping the Gas Turbine, a suitable control system has been developed and programmed in DCS system. The details of the sequence of events, with developed control system, during auto change over of Gas Turbine from "main fuel oil" to "standby fuel oil" are as given below; 1. Gas Turbine is operating on "main fuel oil" (1) 14 2. Pumping system of "standby fuel oil" is in running condition (1) 3. Pressure control valve (4) In the "main fuel oil" forwarding system is in the required high open condition based on the command from the PID controller (8). 4. Pressure control valve (4) in the "standby fuel oil" forwarding system is in the partially open condition. 5. "Gas Turbine load reference signal" is continuously fed to DCS (8- 8) system from Gas Turbine control system (15). 6. Malfunction in the "main fuel oil" forwarding system as detected by low pressure switch, PSL (11) is sensed by the gas Turbine control system. Gas Turbine control system gives command to 3- way valve (12) to divert its position from "main fuel oil" to "standby fuel oil", to enable auto change over of gas turbine from "main fuel oil mode" to "standby fuel oil" mode, with a parallel "main fuel oil to standby fuel oil change over signal to DCS (8-8)". 15 7. The load reference signal from Gas Turbine is continuously available to the DCS "scaling" function (18). The load reference signal indicates the present load on the Gas Turbine at that moment The 'scaling' function contains a 'look-up' table having data for converting toad reference signal into the required pressure control valve opening, corresponding to present load on the Gas Turbine at that moment. On receiving "Main fuel oil" to "standby fuel oil" change over signal from Gas Turbine control system, the "SR" flip flop (19) changes the position of selector switch from position "AC" to position "BC", bypassing the output from "PID" controller. In position "BC" the output of the scaling function is fed to the pressure control valve for a duration of 't' seconds. During the time period of 't' seconds, the pressure control valve will be ramped up to the corresponding percentage of opening, thus enabling successful change over of Gas Turbine. 16 After 't' seconds, the position of the selection switch is changed from "BC" to "AC" by "SR" flip flop, transferring the control of the pressure control valve back to PID controller within DCS. Duration of 't' seconds is set in the "On delay (20) timer" to reset the 'SR' flip flop. BRIEF DECRIPTION OF THE ACCOMPANIED DRAWINGS Fig-1 Illustrates flow diagram of fuel oil supply system of a typical Gas Turbine plant, operating on "main fuel oil" as well as "standby fuel oil". (With conventional PID pressure control system). Flg-2 illustrates flow diagram of fuel oil supply system of a typical Gas Turbine Plant, operating on "main fuel oil" as well as "standby fuel oil". (With fuel oil pressure control system for auto change over from "main fuel oil" to "standby fuel oil" and vice versa of gas turbine on load). 18 WE CLAIM 1. A novel device for automatic control of fuel oil pressure of main and standby fuel injection system simultaneously for a gas turbine plant during on bad condition. 2. The device as claimed under claim (1), wherein an automatic change over means from main fuel oil to stand by fuel oil supply system and vice versa during on load condition of gas turbine plant. 3. The device as claimed under claim (1) & (2), wherein a means of flexibility of using two different fuel oils in the gas turbine plant. 4. The device as claimed under claim (1), (2) & (3) wherein a scaling and tripping device (18) to convert load reference signal into required pressure control valve opening. Dated this 30th day of MARCH 2007 Many Gas Turbine plants operate ON "main fuel oil" as well as "standby fuel oil" to ensure uninterrupted operation. In order to ensure uninterrupted operation of Gas Turbine, due to any problem in the operating fuel oil supply system, it should Be possible for the Gas Turbine to change over to the standby fuel oil system, without interruption in the power generation. It has been observed that present fuel oil pressure control systems with conventional PID controllers are not able to sustain the fuel oil pressure during fuel change over conditions, leading to the trip of the Gas Turbine. A suitable control system has been developed and programmed in DCS system for Fuel oil pressure control system for auto change over from "main fuel oil" to "standby fuel oil" And vice versa of Gas Turbine on load.

Documents:

00528-kol-2007-claims.pdf

00528-kol-2007-correspondence others 1.1.pdf

00528-kol-2007-correspondence others.pdf

00528-kol-2007-description complete.pdf

00528-kol-2007-drawings.pdf

00528-kol-2007-form 1.pdf

00528-kol-2007-form 18.pdf

00528-kol-2007-form 2.pdf

00528-kol-2007-form 3.pdf

00528-kol-2007-gpa.pdf

528-KOL-2007-(02-02-2012)-CORRESPONDENCE.pdf

528-KOL-2007-(02-09-2011)-ABSTRACT.pdf

528-KOL-2007-(02-09-2011)-AMANDED CLAIMS.pdf

528-KOL-2007-(02-09-2011)-CORRESPONDENCE.pdf

528-KOL-2007-(02-09-2011)-DESCRIPTION (COMPLETE).pdf

528-KOL-2007-(02-09-2011)-DRAWINGS.pdf

528-KOL-2007-(02-09-2011)-FORM 1.pdf

528-KOL-2007-(02-09-2011)-FORM 2.pdf

528-KOL-2007-(02-09-2011)-FORM 3.pdf

528-KOL-2007-(02-09-2011)-OTHERS.pdf

528-KOL-2007-(02-09-2011)-PA.pdf

528-KOL-2007-ABSTRACT.pdf

528-KOL-2007-AMANDED CLAIMS.pdf

528-KOL-2007-CORRESPONDENCE 1.1.pdf

528-KOL-2007-CORRESPONDENCE.pdf

528-KOL-2007-DESCRIPTION (COMPLETE).pdf

528-KOL-2007-DRAWINGS.pdf

528-KOL-2007-EXAMINATION REPORT.pdf

528-KOL-2007-FORM 1.pdf

528-KOL-2007-FORM 13 1.1.pdf

528-KOL-2007-FORM 13.pdf

528-KOL-2007-FORM 18.pdf

528-KOL-2007-FORM 2.pdf

528-KOL-2007-FORM 3.pdf

528-KOL-2007-GPA.pdf

528-KOL-2007-GRANTED-ABSTRACT.pdf

528-KOL-2007-GRANTED-CLAIMS.pdf

528-KOL-2007-GRANTED-DESCRIPTION (COMPLETE).pdf

528-KOL-2007-GRANTED-DRAWINGS.pdf

528-KOL-2007-GRANTED-FORM 1.pdf

528-KOL-2007-GRANTED-FORM 2.pdf

528-KOL-2007-GRANTED-LETTER PATENT.pdf

528-KOL-2007-GRANTED-SPECIFICATION.pdf

528-KOL-2007-OTHERS 1.1.pdf

528-KOL-2007-OTHERS 1.3.pdf

528-KOL-2007-OTHERS-1.2.pdf

528-KOL-2007-PA.pdf

528-KOL-2007-REPLY TO EXAMINATION REPORT 1.1.pdf

528-KOL-2007-REPLY TO EXAMINATION REPORT.pdf