US3780705A - Method of controlling the feed of forced circulation steam generators - Google Patents
Method of controlling the feed of forced circulation steam generators Download PDFInfo
- Publication number
- US3780705A US3780705A US00291934A US3780705DA US3780705A US 3780705 A US3780705 A US 3780705A US 00291934 A US00291934 A US 00291934A US 3780705D A US3780705D A US 3780705DA US 3780705 A US3780705 A US 3780705A
- Authority
- US
- United States
- Prior art keywords
- control signal
- signal
- feedwater
- load range
- flow
- 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.)
- Expired - Lifetime
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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
- F22B35/14—Control systems for steam boilers for steam boilers of forced-flow type during the starting-up periods, i.e. during the periods between the lighting of the furnaces and the attainment of the normal operating temperature of the steam boilers
-
- 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
- F22B35/101—Control systems for steam boilers for steam boilers of forced-flow type of once-through type operating with superimposed recirculation during starting or low load periods, e.g. composite boilers
Definitions
- the invention provides a method of controlling the rate of feed of a forced circulation steam generator wherein a first controlled condition acts predominantly on a feedwater flow in a first load range and a second controlled condition acts predominantly on the feedwater flow in a second load range.
- the feedwater flow is controlled by a command signal produced by a predetermined or preset base signal having superimposed thereon in the first load range only the first control signal and only when the first control signal is of the sense to reduce the command signal and having superimposed thereon in the second load range only the second control signal and only when the second control signal is of the sense to increase the command signal.
- the method includes the steps of feeding a flow of feedwater to the steam generator, producing a first control signal in response to the first controlled condition, producing a second control signal in response to the second controlled condition, producing the base signal and of generating the command signal in the first load range by superimposing only the first control signal on the base signal and only when the first control signal is of a sense to reduce the base signal and in the second load range by superimposing only the second control signal on the base signal and only when the second control signal is of a sense to increase the base signal.
- the steam generator is of the kind operated with sliding pressure and the first controlled condition is used in the load range in which steam delivery pressure is subcritical and the second controlled condition is used when the steam delivery pressure is supercritical.
- the invention provides a method in which the change-over between control by the first controlled condition and control by the second controlled condition occurs smoothly and without the two controlled conditions acting simultaneously and in conflict with one another (one demanding more and the other demanding less feed water) and without sudden changes in the control signal which might lead to severe damage due to thermal shock, for example by sudden displacement of the location of the end of the zone in which evaporation takes place or by the ejection of water from the separator into the super-heater.
- the invention allows construction of a control system by which a steam generator can be controlled which is simple and which uses comparatively inexpensive control equipment.
- the invention is particularly suitable for application to forced through-flow steam generators with forced circulation in a limited load range.
- the base signal preferably has a value which is sufficiently high to produce a feed water supply which is sufficient to cool the evaporator of the steam generator at the top of the limited load range.
- FIG. 1 diagrammatically illustrates a forced throughflow steam generator with superimposed circulation controlled in accordance with the invention
- FIG. 2 graphically illustrates the change in the amount of working medium as a function of the load for the steam generator shown in FIG. 1;
- FIG. 3 illustrates a modification of the control system of the steam generator shown in FIG. 1 which is suitable for handling particularly rapid and large disturbancesv
- a steam generator 6 has a feed pump 1 which supplies working medium through a feed line 2, a feed valve 3 and a flow-rate metering position 4 to an economiser 5.
- the water which is preheated in the economiser 5 flows from the economiser 5 through a connecting line 7 and a circulating pump 8 into an evaporator 9 and then enters a water separator 10 as a vapor after being completely evaporated or as a vaporwater mixture which is separated in the separator.
- the separated steam then flows through three superheaters 11, 12 and 13 and a live steam valve 14 to the load (not shown) while the water is returned to the connecting line 7 through a line 20 having a valve 21 therein which is controlled by the water level in the water separator 10 in a manner which is not shown.
- the separator 10 is provided with a level-measuring apparatus 25 of suitable construction.
- the water level measured by the apparatus 25 represents a first controlled condition.
- a temperature measuring means 26 of suitable construction is provided on the connecting line between the first superheater l and the second superheater 2. The temperature measured at this position represents a second controlled condition.
- the output of the level-measuring apparatus 25 is connected to a comparator 27 to deliver a signal thereto representative of the water level in the separator 10.
- the comparator 27 is supplied through a line 28 with a water level set value which is preferably constant.
- An output line from the comparator 27 branches at 29 so that an output signal representative of the difference between the actual water level signal and the set value signal is supplied to a function generator 30 having integral action (hereafter referred to as an I- element) and to a function generator 31 having proportional action (hereafter referred to as a P-element).
- the outputs of the two elements 30 and 31 are combined at position 32 to form a first control signal which is supplied to a limiter 33 which limits the control signal to positive values.
- the temperature actual value signal from the means 26 is compared at a comparator 37 with temperature set value which is supplied through a line 38 and whose magnitude is dependent upon the load or steam delivery pressure.
- a signal representative of the deviation of the actual value signal from the set value signal is supplied via an output line to a branch point 39 and is supplied to an I-element 40 and to a function generator 41 having proportional-plus-derivative action (hereafter referred to-as a PD-elementf).
- the outp.u.ts of the two elements 40 and 41 are added at position 42 and are supplied to a limiter 43.
- the inverse of the output of the limiter 33, the uninverted output of the. limiter 43 and the output of a base signal transmitter 46 are added together and the sum thus formed is supplied in the form of a command signal along a line 47 to a feed controller 48 which actuates the feed valve 3.
- a working medium flow rate signal formed by a flow-rate-measuring device 49 connected to the position 4 is supplied as a measured value to the feed controller 48.
- the base signal transmitter 46 delivers an output signal which is constant in the lower and middle load ranges and which increases approximately linearly relative to the firing rate in the upper load range in which the temperature effect predominates.
- the base signal is constant in the upper load range also.
- the first control signal formed at position 32 and the second control signal formed at position 42 are supplied through lines 50 and 51 to analog-digital converters'52 and 53, respectively. These converters 52, 53, respectively. These converters 52, 53 energize separate relays 54, 55, respectively, if the respective control signals become negative so that the connections between the branching points 29, 39 and the I-elements 30, 40, respectivley, are interrupted This avoids a run-away increase in the output signal from either of the I- elements when it is not in control.
- the base signal transmitter 46 provides a working medium flow rate set value of 60 percent of the amount required at full load. If the steam generator is operated at, for example, a load of 40 percent, excess water will collect in the separator until the first control signal formed at position 32 is sufficiently large to reduce the command signal in line 47 to 40 percent. The second control signal derived from the temperature is negative in the aforementioned load range and thus is ineffective. If the load is gradually increased, the level in the separator 10 will drop and as a result the magnitude of the first control signal, fed in negatively, gradually diminishes while the command signal in line 47 increases.
- the water content of the separator 10 is subsequently gradually lost, partly through the circulating pump 8 and partly by evaporation after the valve 21 is closed.
- the cycle will be performed in the opposite sense.
- the command signal in line 47 diminishes with a diminishing second control signal until the latter becomes zero.
- the command signal then stops at the residual value of the base signal while the separator 10. is full, and thereafter diminishes due to the action of the first control signal.
- the kinked line f shows the characteristic of the feed rate and the curve v indicates the rate of flow of working medium through the evaporator as a function of the load.
- the broken line g relates to the change of base signal while the dash-dot straight line d represents the amount of generated steam.
- the difference in the vertical direction between d and f corresponds to the amount of water which is injected through a duct 15 (FIG. I) to the working medium between the superheaters 12 and 13 and which is adjusted in dependence upon the steam delivery temperature while the difference R between v and f relates to the circulated amount of water.
- the line f has a distinct stopping point extending over the load interval L, to L
- the command signal is formed by subtraction from the base signal (g) of the first control signal corresponding to the difference (g-f) while in the load range above L the command variable is performed by addition to the base signal (g) of the second control signal which corresponds to the difference (f-g).
- While the system shown in FIG. 1 has an excellent control characteristic at medium rates of load change and in conditions of normal disturbances, it is possible for the dynamic characteristics of the system to be improved by refining the control method for conditions of high rates of load change and severe disturbances.
- Such a refinement is obtained if integration by the I-element 30 associated with the first controlled condition is interrupted when both deviations, i.e. the results of the comparisons made by the comparators 27, 37, are negative and if integration by the I-element 40 associated with the second controlled condition is interrupted when both deviations are positive.
- the width of the interval L to L which may be adjusted by variation of the set value 38, may thus be reduced.
- FIG. 3 shows a part of the control system shown in FIG. 1 with elaborations by means of which the refined method may be performed.
- analog-digital converters and 61 are connected to the output lines from the comparators to form separate digital signals from the deviations formed by the comparators 27 and 37, each digital signal changing from 0 to 1 if the respective deviation changes its sign from negative to positive and vice versa.
- the outputs of the two converters act on an OR element 64 and on an AND element 65, respectively.
- the inverted output of the OR element 64 acts on a relay 66, the contact set of which is connected in series with the contact set of the relay 54 in the feed of the I-element 30.
- the output of the AND element 65 acts uninverted on a relay 67, the contact set of which is connected in series with the contact set of the relay 55 in the feed of the l-element 40.
- the circulating pump 8 may be arranged to operate only when the load is below a predetermined proportion of full load.
- the base signal delivered by the transmitter 46 should be sufficiently high to insure that immediately after the pump 8 shuts off should the load increase above this proportion, the flow of feed-water through the valve 3 will be high enough to adequately cool the evaporator 9.
- a method of controlling a rate of feed of water in a forced circulation steam generator comprising the steps of feeding a flow of feedwater to the steam generator;
- said first controlled condition is the water level in a water-steam separator in the steam generator in the flow path of the feedwater and said second controlled condition is the steam temperature of the steam generated from the feedwater downstream of a superheater in the steam generator.
- said first control signal is formed by a separate controller having integral action from a signal responsive to said first controlled condition and which further comprises the 7 step of blocking integration by the controller as soon as said first control signal becomes negative.
- said second control signal is formed by a separate controller having integral action from a signal responsive to said second controlled condition and which further comprises the step of blocking integration by the controller as soon as said second control signal becomes negative.
- said first control signal is formed by a second separate controller having integral action from a signal responsive to said first controlled condition and which further comprises the steps of blocking integration by the second controller as soon as said first control signal becomes negative, of blocking integration by one of the controllers when the signals supplied to the controllers are both positive and of blocking integration by the other of the controllers when the signals supplied to the controllers are both negative.
- a steam generator having a feed controller for controlling the rate of feedwater flow to an evaporator, a water separator downstream of said evaporator and at least one superheater downstream of said water separator; means for controlling said feed controller to control the rate of flow of the feedwater, saidmeans including a water-level measuring means connected to said separator to produce a first control signal in response to the level of water in said separator, a steam temperature measuring means downstream of said superheater to produce a second control signal in response to the temperature of the steam thereat, a base signal transmitter for emitting a predetermined base signal, and means for superimposing said base signal with only said first control signal in a first load range when said first control signal is negative relative to said base signal and with only said second control signal in a second load range when said second control signal is positive relative to said base signal for producing a command signal, said latter means being connected to said feed controller to deliver said command signal thereto for adjustment of the rate of feedwater flow in response thereto.
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Control Of Steam Boilers And Waste-Gas Boilers (AREA)
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CH1396871A CH532750A (de) | 1971-09-24 | 1971-09-24 | Verfahren zur Speiseregelung eines Zwangdurchlauf-Dampferzeugers |
Publications (1)
Publication Number | Publication Date |
---|---|
US3780705A true US3780705A (en) | 1973-12-25 |
Family
ID=4396839
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US00291934A Expired - Lifetime US3780705A (en) | 1971-09-24 | 1972-09-25 | Method of controlling the feed of forced circulation steam generators |
Country Status (12)
Country | Link |
---|---|
US (1) | US3780705A (xx) |
JP (1) | JPS539321B2 (xx) |
BE (1) | BE788957A (xx) |
CA (1) | CA963558A (xx) |
CH (1) | CH532750A (xx) |
DE (1) | DE2149127B1 (xx) |
ES (1) | ES406840A1 (xx) |
FR (1) | FR2154241A5 (xx) |
GB (1) | GB1410181A (xx) |
IT (1) | IT967803B (xx) |
NL (1) | NL145342B (xx) |
SE (1) | SE381504B (xx) |
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4242989A (en) * | 1979-05-14 | 1981-01-06 | General Electric Company | Boiler level control system |
FR2489480A1 (fr) * | 1980-09-02 | 1982-03-05 | Gen Electric | Dispositif de commande du niveau d'eau d'un deaerateur |
US4619224A (en) * | 1984-08-17 | 1986-10-28 | Hitachi, Ltd. | Apparatus for controlling drum water level of drum type boiler |
US20060065266A1 (en) * | 2004-09-30 | 2006-03-30 | Atul Saksena | Steam cooker and related superheater |
US20060107943A1 (en) * | 2004-11-24 | 2006-05-25 | Atul Saksena | Steam oven system having steam generator with controlled fill process |
WO2009101075A2 (de) * | 2008-02-15 | 2009-08-20 | Siemens Aktiengesellschaft | Verfahren zum anfahren eines durchlaufdampferzeugers |
Families Citing this family (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5094025A (xx) * | 1973-12-24 | 1975-07-26 | ||
JPS5193926A (xx) * | 1975-02-15 | 1976-08-18 | ||
JPS5236173A (en) * | 1975-09-17 | 1977-03-19 | Takasaki Paper Mfg | Process for manufacturing tile assemblage mainly from wood pulp |
JPS55180102U (xx) * | 1979-06-09 | 1980-12-24 | ||
US4424186A (en) * | 1981-03-02 | 1984-01-03 | Westinghouse Electric Corp. | Power generation |
JPS5869437U (ja) * | 1981-11-02 | 1983-05-11 | 株式会社イナックス | タイル |
TW212826B (xx) * | 1991-11-28 | 1993-09-11 | Sulzer Ag | |
DE19536391A1 (de) * | 1995-09-29 | 1997-04-03 | Siemens Ag | Vorrichtung zur Regelung des Pegels einer in einem Vorratsbehälter aufgenommenen Flüssigkeit |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3042007A (en) * | 1958-07-28 | 1962-07-03 | Beckman Instruments Inc | Boiler controller |
US3215126A (en) * | 1960-12-19 | 1965-11-02 | Babcock & Wilcox Co | Once-through vapor generator |
US3244898A (en) * | 1959-12-29 | 1966-04-05 | Combustion Eng | Power plant system and control therefor |
US3452722A (en) * | 1966-12-30 | 1969-07-01 | Sulzer Ag | Positively operated steam generator |
-
0
- BE BE788957D patent/BE788957A/xx not_active IP Right Cessation
-
1971
- 1971-09-24 CH CH1396871A patent/CH532750A/de not_active IP Right Cessation
- 1971-10-01 DE DE19712149127D patent/DE2149127B1/de active Pending
- 1971-10-20 NL NL717114443A patent/NL145342B/xx not_active IP Right Cessation
-
1972
- 1972-09-18 GB GB4309972A patent/GB1410181A/en not_active Expired
- 1972-09-19 ES ES406840A patent/ES406840A1/es not_active Expired
- 1972-09-20 JP JP9447272A patent/JPS539321B2/ja not_active Expired
- 1972-09-22 FR FR7233782A patent/FR2154241A5/fr not_active Expired
- 1972-09-22 CA CA152,351A patent/CA963558A/en not_active Expired
- 1972-09-22 SE SE7212291A patent/SE381504B/xx unknown
- 1972-09-23 IT IT29600/72A patent/IT967803B/it active
- 1972-09-25 US US00291934A patent/US3780705A/en not_active Expired - Lifetime
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3042007A (en) * | 1958-07-28 | 1962-07-03 | Beckman Instruments Inc | Boiler controller |
US3244898A (en) * | 1959-12-29 | 1966-04-05 | Combustion Eng | Power plant system and control therefor |
US3215126A (en) * | 1960-12-19 | 1965-11-02 | Babcock & Wilcox Co | Once-through vapor generator |
US3452722A (en) * | 1966-12-30 | 1969-07-01 | Sulzer Ag | Positively operated steam generator |
Cited By (14)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4242989A (en) * | 1979-05-14 | 1981-01-06 | General Electric Company | Boiler level control system |
FR2489480A1 (fr) * | 1980-09-02 | 1982-03-05 | Gen Electric | Dispositif de commande du niveau d'eau d'un deaerateur |
US4345438A (en) * | 1980-09-02 | 1982-08-24 | General Electric Company | Deaerator level control |
US4619224A (en) * | 1984-08-17 | 1986-10-28 | Hitachi, Ltd. | Apparatus for controlling drum water level of drum type boiler |
US20080271612A1 (en) * | 2004-09-30 | 2008-11-06 | Premark Feg L.L.C. | Steam cooker and related superheater |
US20060065266A1 (en) * | 2004-09-30 | 2006-03-30 | Atul Saksena | Steam cooker and related superheater |
US8111072B2 (en) * | 2004-09-30 | 2012-02-07 | Premark Feg L.L.C. | Steam cooker and related superheater |
US7418960B2 (en) | 2004-09-30 | 2008-09-02 | Premark Feg Llc | Steam cooker and related superheater |
US7353821B2 (en) | 2004-11-24 | 2008-04-08 | Premark Feg L.L.C. | Steam oven system having steam generator with controlled fill process |
US20060107943A1 (en) * | 2004-11-24 | 2006-05-25 | Atul Saksena | Steam oven system having steam generator with controlled fill process |
WO2009101075A2 (de) * | 2008-02-15 | 2009-08-20 | Siemens Aktiengesellschaft | Verfahren zum anfahren eines durchlaufdampferzeugers |
EP2119880A1 (de) * | 2008-02-15 | 2009-11-18 | Siemens Aktiengesellschaft | Verfahren zum Anfahren eines Durchdampferzeugers |
WO2009101075A3 (de) * | 2008-02-15 | 2009-12-23 | Siemens Aktiengesellschaft | Verfahren zum anfahren eines durchlaufdampferzeugers |
US9810101B2 (en) | 2008-02-15 | 2017-11-07 | Siemens Aktiengesellschaft | Method for starting a continuous steam generator |
Also Published As
Publication number | Publication date |
---|---|
FR2154241A5 (xx) | 1973-05-04 |
SE381504B (sv) | 1975-12-08 |
CH532750A (de) | 1973-01-15 |
JPS4839801A (xx) | 1973-06-12 |
IT967803B (it) | 1974-03-11 |
NL145342B (nl) | 1975-03-17 |
ES406840A1 (es) | 1975-11-16 |
NL7114443A (xx) | 1973-03-27 |
JPS539321B2 (xx) | 1978-04-05 |
GB1410181A (en) | 1975-10-15 |
CA963558A (en) | 1975-02-25 |
BE788957A (fr) | 1973-03-19 |
DE2149127B1 (de) | 1972-11-09 |
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