EP0065408A2 - Control systems for boilers - Google Patents
Control systems for boilers Download PDFInfo
- Publication number
- EP0065408A2 EP0065408A2 EP82302398A EP82302398A EP0065408A2 EP 0065408 A2 EP0065408 A2 EP 0065408A2 EP 82302398 A EP82302398 A EP 82302398A EP 82302398 A EP82302398 A EP 82302398A EP 0065408 A2 EP0065408 A2 EP 0065408A2
- Authority
- EP
- European Patent Office
- Prior art keywords
- boiler
- phase
- pressure
- valve
- valve means
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
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Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F22—STEAM GENERATION
- F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
- F22B35/00—Control systems for steam boilers
- F22B35/06—Control systems for steam boilers for steam boilers of forced-flow type
- F22B35/10—Control systems for steam boilers for steam boilers of forced-flow type of once-through type
- F22B35/105—Control systems for steam boilers for steam boilers of forced-flow type of once-through type operating at sliding pressure
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F22—STEAM GENERATION
- F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
- F22B35/00—Control systems for steam boilers
- F22B35/06—Control systems for steam boilers for steam boilers of forced-flow type
- F22B35/10—Control systems for steam boilers for steam boilers of forced-flow type of once-through type
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
- F01K3/00—Plants characterised by the use of steam or heat accumulators, or intermediate steam heaters, therein
- F01K3/18—Plants characterised by the use of steam or heat accumulators, or intermediate steam heaters, therein having heaters
- F01K3/20—Plants characterised by the use of steam or heat accumulators, or intermediate steam heaters, therein having heaters with heating by combustion gases of main boiler
- F01K3/22—Controlling, e.g. starting, stopping
Definitions
- the present invention relates to control systems for boilers.
- variable pressure boiler system In a variable pressure boiler system, the throttle pressure varies with the load. In its ideal form, the throttle valves on the turbine are left wide open and the throttle pressure varies directly with the load. Such variable pressure operation is desirable since it can increase the efficiency of the turbine.
- the primary incentive for variable pressure operation is that it can increase the number of times that the turbine can be loaded and unloaded. This is because, with variable pressure operation, the change in the first stage steam exit temperature in the turbine is relatively minor, thus minimising thermal stress in the metal comprising the turbine.
- the first stage steam exit temperature is load dependent. This can result in a greater change in temperature for the turbine which, in turn, can cause excessive metal fatigue.
- a control system for a boiler being characterised by first valve means operable during a first phase of operation of the system, second valve means in fluidic communication with the first valve means and operable to open to a predetermined position during the first phase of operation of the system, and third valve means in fluidic communication with the second valve means and operable to vary the flow of steam from the boiler in response to the load imposed on the system during a second phase of operation of the system.
- a preferred embodiment of the present invention described below solves or at least alleviates the aforementioned problems associated with the prior art by providing a boiler control system in which variable throttle pressure operation can be introduced at as low a load as possible and can be utilised for most of the load operating range. This is accomplished by opening a turbine valve to approximately 70 percent of its fully open position as soon as possible as the system is being loaded, utilising a flash tank while this is occurring unti the load demand exceeds minimum feedwater flow requirements, and then allowing the system to assume the variable throttle pressure mode of operation as the load is increased until throttle pressure approximates a designed operating pressure, at which time the turbine valve is regulated to meet load requirements.
- the preferred system provides for variable pressure operation from approximately 20 percent to 75 percent of load and also provides for smooth transition from low load operation to the variable pressure mode of operation, and from the variable pressure mode of operation to a full pressure mode of operation.
- a control coordinator is provided to monitor and correct steam flow, firing rate and feedwater flow. In this manner, the system can automatically adjust and compensate for deviations in these parameters from that which is desired.
- the preferred control system thus permits variable throttle pressure operation of a once-through boiler, enables a once-through boiler to be operated in a variable pressure mode of operation over a wide load range, and provides a smooth transition in a once-through boiler from a low load type of operation to a variable pressure mode of operation and from the variable pressure mode of operation to a full pressure mode of operation.
- FIG. 1 is a schematic drawing of a system 10 embodying the present invention.
- the system 10 comprises primarily a furnace 12 whose output is connected to an input to a primary superheater 14, a flash tank 16, a secondary superheater 18 whose output is connected to an input to a turbine 20 via a turbine valve 22, a generator 23, and a condenser 24.
- the condenser 24 is connected to an input to the furnace 12 via a low pressure heater 26, deaerator 28, a boiler feed pump 30, and a high pressure heater 32.
- the primary superheater 14 is connected to an input to the flash tank 16 via a valve 34 and the flash tank 16 is connected to the secondary superheater 18 via a valve 36.
- a pair of valves 38 and 40 are conected in parallel across the input to the valve 34 and an output of the valve 36.
- a valve 42 is provided between the flash tank 16 and the condenser 24 and controls the flow of water from the flash tank 16 to the condenser.
- a superheated steam attemperator valve 44 is provided between the output of the secondary superheater 18 and the flash tank 16.
- FIG. 2 The principle of operation of the system is shown in Figure 2.
- percentage pressure or valve opening is plotted versus percentage load, and flash tank pressure, furnace pressure, turbine valve position and throttle pressure are illustrated.
- the objective is to obtain variable .throttle pressure at as low a load as possible, provide a smooth transition from low load operation to once-through operation, and incorporate the capabilities of a control coordinator 50, shown in Figure 3, during a variable throttle pressure phase of operation. This is accomplished by opening the turbine valve 22 as soon as possible, by operating the flash tank 16 until it is dry, and by using the valves 38 and 40 between the primary superheater 14 and the secondary superheater 18 as throttle valves, as wil hereinafter be described.
- a unique feature of this control strategy is that throttle pressure is not directly controlled, except at minimum pressure, but is permitted to float to whatever level is required for the desired load. Thus, variable pressure operation is achieved over a very substantial portion of the load range.
- an incoming control signal is applied to a unit load demand development function 52, an output of which is directed to the control coordinator 50 and to a turbine valve program 54, a steam flow modifier 56, a firing rate modifier 58, a feedwater modifier 60, and controls for the valve 36.
- the turbine valve program 54 controls the operation of the turbine valve 22
- the steam flow modifier 56 controls the operation of the valves 38 and 40
- the firing rate modifier 50 controls the fuel and air mixture in the system
- the feedwater modifier 60 regulates the flow of feedwater throughout the system.
- a pressure transmitter 62 is connected to both the control coordinator 50 and the control valve 34, and an electrical transmitter 64, a feedwater temperature transmitter 66 and a superheater temperature transmitter 68 are also connected as inputs to the control coordinator 50 which, in turn, regulates the steam flow modifier 56, the firing rate modifier 58 and the feedwater modifier 60 by means of control signals generated therein.
- the control system has basically three modes of operation: low load operation, once-through variable pressure operation, and full pressure operation.
- Low load operation occurs when the boiler feedwater flow is limited to a minimum flow rate.
- Once-through variable pressure operation occurs when the feedwater flow rate exceeds its minimum flow rate and continues until throttle pressure reaches a full design pressure, i.e. furnace pressure.
- Full pressure operation occurs when the throttle pressure has reached full design pressure and continues until full load is achieved.
- the throttle pressure is maintained constant and the turbine valve 22 is rapidly opened to approximately 70 percent of its fully open position, as shown in Figure 2.
- the valves 38 and 40 are closed and the valves 34 and 36, along with the turbine valve 22, are opened.
- the valve 34 controls the furnace pressure
- the valve 36 controls the throttle pressure.
- the valve 42 is also opened and regulates the water level in the flash tank 16.
- all flow from the furnace 12 is directed to the flash tank 16 and starts as water and, as firing is increased, becomes steam.
- the flash tank 16 acts as a steam and water separator and directs the water to the condenser 24 and the steam to the turbine 20.
- the valve 40 opens and the valves 34 and 36 start closing, stopping the flow to the flash tank 16. This occurs at approximately 25 percent of load and starts the next phase of operation, i.e. the variable throttle pressure phase or once-through variable pressure phase of operation.
- variable pressure phase or variable throttle pressure phase of operation the turbine valve 22 is maintained at approximately 70 percent of its fully open position by the turbine valve program 54.
- steam flow control is regulated by the valve 40 and this valve, in essence, acts as a remote throttle valve.
- the feedwater flow is given the responsibility of controlling steam temperature, whereas the firing rate controls the load, and throttle pressure is permittted to float to whatever value is necessary to satisfy the load requirements.
- the control coordinator 50 assumes an important function in this phase of operation since it produces error or correction signals to the steam flow modifier 56, the firing rate modifier 58 and the feedwater modifier 60.
- error or correction signals are as follows: a megawatt error minus a furnace pressure error control signal which is directed to the steam flow modifier 56, a megawatt error plus a furnace pressure error control signal which is directed to the firing rate modifier 58, and a superheat temperature error plus a feedwater temperature control signal which is directed to the feedwater modifier 60.
- the feedwater flow can be adjusted to maintain steam temperature while the steam flow and the firing rate can be corrected to maintain proper furnace pressure and megawatts.
- valve 38 When the valve 40 approaches its fully open position, the valve 38 starts opening and the turbine valve 22 is permitted to start opening further from its 70 percent open position. This commences the next phase of operation, i.e. the full pressure phase of operation.
- control system produces a number of benefits. For example, by using variable pressure the first stage steam temperature can be closely controlled, which permits rapid loading of the turbine without creating excessive thermal stress.
- the foregoing system provides for quickly achieving variable pressure operation, turbine metal temperature matching, and a smooth transition to once-through operation.
- control coordinator regulates and controls the overall operation of the system in the variable pressure phase of operation and adjusts the system components to compensate for various operational deviations.
Abstract
Description
- The present invention relates to control systems for boilers.
- In a variable pressure boiler system, the throttle pressure varies with the load. In its ideal form, the throttle valves on the turbine are left wide open and the throttle pressure varies directly with the load. Such variable pressure operation is desirable since it can increase the efficiency of the turbine. However, the primary incentive for variable pressure operation is that it can increase the number of times that the turbine can be loaded and unloaded. This is because, with variable pressure operation, the change in the first stage steam exit temperature in the turbine is relatively minor, thus minimising thermal stress in the metal comprising the turbine. In contrast, in a constant pressure type of operation, the first stage steam exit temperature is load dependent. This can result in a greater change in temperature for the turbine which, in turn, can cause excessive metal fatigue.
- Because of the foregoing, it has become desirable to develop a control system for the operation of a once-through boiler so that a variable throttle pressure type of operation can be utilised over a very wide load range.
- According to the present invention there is provided a control system for a boiler, the system being characterised by first valve means operable during a first phase of operation of the system, second valve means in fluidic communication with the first valve means and operable to open to a predetermined position during the first phase of operation of the system, and third valve means in fluidic communication with the second valve means and operable to vary the flow of steam from the boiler in response to the load imposed on the system during a second phase of operation of the system.
- A preferred embodiment of the present invention described below solves or at least alleviates the aforementioned problems associated with the prior art by providing a boiler control system in which variable throttle pressure operation can be introduced at as low a load as possible and can be utilised for most of the load operating range. This is accomplished by opening a turbine valve to approximately 70 percent of its fully open position as soon as possible as the system is being loaded, utilising a flash tank while this is occurring unti the load demand exceeds minimum feedwater flow requirements, and then allowing the system to assume the variable throttle pressure mode of operation as the load is increased until throttle pressure approximates a designed operating pressure, at which time the turbine valve is regulated to meet load requirements. In essence, the preferred system provides for variable pressure operation from approximately 20 percent to 75 percent of load and also provides for smooth transition from low load operation to the variable pressure mode of operation, and from the variable pressure mode of operation to a full pressure mode of operation. In addition, while in the variable pressure mode of operation, a control coordinator is provided to monitor and correct steam flow, firing rate and feedwater flow. In this manner, the system can automatically adjust and compensate for deviations in these parameters from that which is desired.
- The preferred control system thus permits variable throttle pressure operation of a once-through boiler, enables a once-through boiler to be operated in a variable pressure mode of operation over a wide load range, and provides a smooth transition in a once-through boiler from a low load type of operation to a variable pressure mode of operation and from the variable pressure mode of operation to a full pressure mode of operation.
- The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which:
- Figure 1 is a schematic diagram of a system embodying the present invention;
- Figure 2 is a graph of percentage pressure or valve opening versus percentage load for the system and illustrates flash tank pressure, furnace pressure, turbine valve position and throttle pressure; and
- Figure 3 is a schematic diagram which illustrates the overall system.
- Figure 1 is a schematic drawing of a
system 10 embodying the present invention. Thesystem 10 comprises primarily afurnace 12 whose output is connected to an input to aprimary superheater 14, aflash tank 16, asecondary superheater 18 whose output is connected to an input to aturbine 20 via aturbine valve 22, agenerator 23, and acondenser 24. Thecondenser 24 is connected to an input to thefurnace 12 via alow pressure heater 26,deaerator 28, aboiler feed pump 30, and ahigh pressure heater 32. - The
primary superheater 14 is connected to an input to theflash tank 16 via avalve 34 and theflash tank 16 is connected to thesecondary superheater 18 via avalve 36. A pair ofvalves valve 34 and an output of thevalve 36. Avalve 42 is provided between theflash tank 16 and thecondenser 24 and controls the flow of water from theflash tank 16 to the condenser. A superheatedsteam attemperator valve 44 is provided between the output of thesecondary superheater 18 and theflash tank 16. - The principle of operation of the system is shown in Figure 2. In Figure 2, percentage pressure or valve opening is plotted versus percentage load, and flash tank pressure, furnace pressure, turbine valve position and throttle pressure are illustrated. The objective is to obtain variable .throttle pressure at as low a load as possible, provide a smooth transition from low load operation to once-through operation, and incorporate the capabilities of a
control coordinator 50, shown in Figure 3, during a variable throttle pressure phase of operation. This is accomplished by opening theturbine valve 22 as soon as possible, by operating theflash tank 16 until it is dry, and by using thevalves primary superheater 14 and thesecondary superheater 18 as throttle valves, as wil hereinafter be described. A unique feature of this control strategy is that throttle pressure is not directly controlled, except at minimum pressure, but is permitted to float to whatever level is required for the desired load. Thus, variable pressure operation is achieved over a very substantial portion of the load range. - In order to accomplish the foregoing, the system is organised in accordance with a schematic illustrated in Figure 3. In Figure 3, an incoming control signal is applied to a unit load
demand development function 52, an output of which is directed to thecontrol coordinator 50 and to aturbine valve program 54, asteam flow modifier 56, afiring rate modifier 58, afeedwater modifier 60, and controls for thevalve 36. Theturbine valve program 54 controls the operation of theturbine valve 22, thesteam flow modifier 56 controls the operation of thevalves firing rate modifier 50 controls the fuel and air mixture in the system, and thefeedwater modifier 60 regulates the flow of feedwater throughout the system. Apressure transmitter 62 is connected to both thecontrol coordinator 50 and thecontrol valve 34, and anelectrical transmitter 64, afeedwater temperature transmitter 66 and asuperheater temperature transmitter 68 are also connected as inputs to thecontrol coordinator 50 which, in turn, regulates thesteam flow modifier 56, thefiring rate modifier 58 and thefeedwater modifier 60 by means of control signals generated therein. - The control system has basically three modes of operation: low load operation, once-through variable pressure operation, and full pressure operation. Low load operation occurs when the boiler feedwater flow is limited to a minimum flow rate. Once-through variable pressure operation occurs when the feedwater flow rate exceeds its minimum flow rate and continues until throttle pressure reaches a full design pressure, i.e. furnace pressure. Full pressure operation occurs when the throttle pressure has reached full design pressure and continues until full load is achieved.
- During the low load phase of operation, i..e. between 0 and approximately 25 percent load, the throttle pressure is maintained constant and the
turbine valve 22 is rapidly opened to approximately 70 percent of its fully open position, as shown in Figure 2. In this mode of operation, thevalves valves turbine valve 22, are opened. Thevalve 34 controls the furnace pressure, whereas thevalve 36 controls the throttle pressure. Thevalve 42 is also opened and regulates the water level in theflash tank 16. During this phase of operation, all flow from thefurnace 12 is directed to theflash tank 16 and starts as water and, as firing is increased, becomes steam. Theflash tank 16 acts as a steam and water separator and directs the water to thecondenser 24 and the steam to theturbine 20. By the time steam flow to theturbine 20 equals the minimum feedwater flow rate of approximately 25 percent, theflash tank 16 has dried up. At that time, thevalve 40 opens and thevalves flash tank 16. This occurs at approximately 25 percent of load and starts the next phase of operation, i.e. the variable throttle pressure phase or once-through variable pressure phase of operation. - In the once-through variable pressure phase or variable throttle pressure phase of operation, the
turbine valve 22 is maintained at approximately 70 percent of its fully open position by theturbine valve program 54. During this phase of operation, steam flow control is regulated by thevalve 40 and this valve, in essence, acts as a remote throttle valve. In this phase of operation, the feedwater flow is given the responsibility of controlling steam temperature, whereas the firing rate controls the load, and throttle pressure is permittted to float to whatever value is necessary to satisfy the load requirements. Thecontrol coordinator 50 assumes an important function in this phase of operation since it produces error or correction signals to thesteam flow modifier 56, thefiring rate modifier 58 and thefeedwater modifier 60. These error or correction signals are as follows: a megawatt error minus a furnace pressure error control signal which is directed to thesteam flow modifier 56, a megawatt error plus a furnace pressure error control signal which is directed to thefiring rate modifier 58, and a superheat temperature error plus a feedwater temperature control signal which is directed to thefeedwater modifier 60. In this manner, the feedwater flow can be adjusted to maintain steam temperature while the steam flow and the firing rate can be corrected to maintain proper furnace pressure and megawatts. - When the
valve 40 approaches its fully open position, thevalve 38 starts opening and theturbine valve 22 is permitted to start opening further from its 70 percent open position. This commences the next phase of operation, i.e. the full pressure phase of operation. - In the full pressure phase of operation, the throttle pressure reaches full design pressure and the
turbine valve 22 is allowed to open still further to maintain the load as is necessary. In this mode of operation, the steam flow is controlled by theturbine valve 22 rather than by thevalve 40, and the combined capacity of thevalves turbine valve 22 is it opens further from its 70 percent open position. It should be noted that with respect to non-variable pressure once-through boiler systems, as in the prior art, this is the normal mode of operation once above the minimum feedwater flow rate, and thus, a variable pressure phase is never introduced therein. - The foregoing control system produces a number of benefits. For example, by using variable pressure the first stage steam temperature can be closely controlled, which permits rapid loading of the turbine without creating excessive thermal stress. In addition, the foregoing system provides for quickly achieving variable pressure operation, turbine metal temperature matching, and a smooth transition to once-through operation. Further, the control coordinator regulates and controls the overall operation of the system in the variable pressure phase of operation and adjusts the system components to compensate for various operational deviations.
Claims (7)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US26284481A | 1981-05-12 | 1981-05-12 | |
US262844 | 1981-05-12 |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0065408A2 true EP0065408A2 (en) | 1982-11-24 |
EP0065408A3 EP0065408A3 (en) | 1983-11-16 |
EP0065408B1 EP0065408B1 (en) | 1986-04-23 |
Family
ID=22999306
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP82302398A Expired EP0065408B1 (en) | 1981-05-12 | 1982-05-11 | Control systems for boilers |
Country Status (8)
Country | Link |
---|---|
EP (1) | EP0065408B1 (en) |
JP (1) | JPS57198902A (en) |
KR (1) | KR870001505B1 (en) |
AU (1) | AU556280B2 (en) |
CA (1) | CA1211324A (en) |
DE (1) | DE3270729D1 (en) |
ES (1) | ES8400580A1 (en) |
MX (1) | MX152206A (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1985002667A1 (en) * | 1983-12-06 | 1985-06-20 | Vsesojuzny Nauchno-Issledovatelsky I Proektno-Kons | Device for recirculation of boiler medium |
KR102210866B1 (en) * | 2019-09-18 | 2021-02-04 | 한국에너지기술연구원 | Generating cycle system using flash tank |
CN113432105A (en) * | 2021-07-14 | 2021-09-24 | 鞍山阿尔肯科技发展有限公司 | Gas boiler heat energy management system under thing networking framework |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3286466A (en) * | 1964-04-24 | 1966-11-22 | Foster Wheeler Corp | Once-through vapor generator variable pressure start-up system |
US3572036A (en) * | 1968-10-21 | 1971-03-23 | Foster Wheeler Corp | Vapor generator start-up system |
US4241585A (en) * | 1978-04-14 | 1980-12-30 | Foster Wheeler Energy Corporation | Method of operating a vapor generating system having integral separators and a constant pressure furnace circuitry |
-
1982
- 1982-05-04 KR KR8201958A patent/KR870001505B1/en active
- 1982-05-10 ES ES512051A patent/ES8400580A1/en not_active Expired
- 1982-05-10 CA CA000402639A patent/CA1211324A/en not_active Expired
- 1982-05-11 AU AU83572/82A patent/AU556280B2/en not_active Ceased
- 1982-05-11 DE DE8282302398T patent/DE3270729D1/en not_active Expired
- 1982-05-11 EP EP82302398A patent/EP0065408B1/en not_active Expired
- 1982-05-12 JP JP57078487A patent/JPS57198902A/en active Granted
- 1982-05-12 MX MX192647A patent/MX152206A/en unknown
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3286466A (en) * | 1964-04-24 | 1966-11-22 | Foster Wheeler Corp | Once-through vapor generator variable pressure start-up system |
US3572036A (en) * | 1968-10-21 | 1971-03-23 | Foster Wheeler Corp | Vapor generator start-up system |
US4241585A (en) * | 1978-04-14 | 1980-12-30 | Foster Wheeler Energy Corporation | Method of operating a vapor generating system having integral separators and a constant pressure furnace circuitry |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1985002667A1 (en) * | 1983-12-06 | 1985-06-20 | Vsesojuzny Nauchno-Issledovatelsky I Proektno-Kons | Device for recirculation of boiler medium |
US4608945A (en) * | 1983-12-06 | 1986-09-02 | Vsesojuzny Nauchno-Issledovatelsky Institut Atomnogo Energeticheskogo Mashinostroenia | Apparatus for recirculating boiler fluid |
KR102210866B1 (en) * | 2019-09-18 | 2021-02-04 | 한국에너지기술연구원 | Generating cycle system using flash tank |
WO2021054586A1 (en) * | 2019-09-18 | 2021-03-25 | 한국에너지기술연구원 | Power generation cycle system using flash tank and control method therefor |
CN113432105A (en) * | 2021-07-14 | 2021-09-24 | 鞍山阿尔肯科技发展有限公司 | Gas boiler heat energy management system under thing networking framework |
Also Published As
Publication number | Publication date |
---|---|
MX152206A (en) | 1985-06-07 |
AU8357282A (en) | 1982-11-18 |
KR830010338A (en) | 1983-12-30 |
ES512051A0 (en) | 1983-11-01 |
JPS57198902A (en) | 1982-12-06 |
CA1211324A (en) | 1986-09-16 |
DE3270729D1 (en) | 1986-05-28 |
KR870001505B1 (en) | 1987-08-19 |
EP0065408B1 (en) | 1986-04-23 |
ES8400580A1 (en) | 1983-11-01 |
EP0065408A3 (en) | 1983-11-16 |
JPS6252122B2 (en) | 1987-11-04 |
AU556280B2 (en) | 1986-10-30 |
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