CN102080820B - Optimal energy-saving method for controlling surface pollutant discharge of steam boiler - Google Patents
Optimal energy-saving method for controlling surface pollutant discharge of steam boiler Download PDFInfo
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- CN102080820B CN102080820B CN2011100017723A CN201110001772A CN102080820B CN 102080820 B CN102080820 B CN 102080820B CN 2011100017723 A CN2011100017723 A CN 2011100017723A CN 201110001772 A CN201110001772 A CN 201110001772A CN 102080820 B CN102080820 B CN 102080820B
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Abstract
The invention discloses an optimal energy-saving method for controlling the surface pollutant discharge of a steam boiler. The method comprises the steps of firstly controlling the flow of pollutant discharge according to the steam flow proportionally, and continuously diluting water in the steam boiler as required; on this basis, configuring a conductivity close loop control circuit to prevent the influences, such as water supply salinity fluctuation, flow rate measurement error, boiler bottom periodic pollutant discharge and the like, and coupling the both by an addition logic unit so as to form a feedforward-feedback complex control system. The invention can prevent various interferences, stably keep the salinity of the water in the steam boiler above the desired level, and realize the optimal energy-saving and emission-reducing effects by the least pollutant discharge amount.
Description
Technical field:
The invention belongs to the boiler energy-saving emission-reduction field, be used for the surface blow-off control of steam boiler.Target is with minimum blowdown flow rate, control pot water salt concentration near and do not exceed allowable value, guarantee that the steam quality of output is up to standard, boiler safety, economical operation.
Background technology:
Steam boiler is in operation, and along with the output of steam, pot water is concentrated.When salinity was elevated to a certain degree, pot water can produce foam, and priming takes place, and steam is with water in a large number, and causes serious false water level, made working of a furnace control unstable.Therefore the salt concentration of pot water be must control, quality of steam and boiler operatiopn safety guaranteed.
There is national standard in China to Industrial Boiler water quality, in GB1576-2001, is the steam boiler of 1.6～2.5Mpa, band superheater to pressure for example, and the dissolved solid concentration (TDS) of regulation pot water must not surpass 2500mg/L.Wherein, dissolved solid can be similar to and think a pot water salt content.
The main method of control pot water salt content is; Be in operation along with the output of steam, adopt the way of surface blow-off, discharge the high pot water of a part of salinity at the downside of drum evaporating surface; And the low make-up water of corresponding additional salinity, realize dilution to pot water salinity.If blowdown flow rate is not enough, the salinity of pot water can be increasingly high; Otherwise, if blowdown flow rate is excessive, be the pot water that contains great amount of heat energy then because of what discharge, can cause the waste of energy loss and soft water resource.The optimal case of energy-saving and emission-reduction is the blowdown flow rates with minimum, and the control boiler water quality is up to standard, guarantees safe operation, improves the thermal efficiency.
The domestic majority Industrial Boiler adopts artificial regularly (per tour once or several times) to measure a pot water salinity with chemical analysis, and manual work opens or closes blowoff valve then.This traditional method for discharging pollution can not the continuous detecting change of water quality, can't realize the control as required of blowdown flow rate.In the face of the variation of steam flow,, can only cause energy waste by the potential evaporation excess discharging of maximum for guaranteeing that water quality does not exceed standard in twice chemical examination at interval.Even so, cannot say for sure still that when load variations is big card pot water is necessarily qualified.
For realizing continuous blowdown as required, both at home and abroad all at the research autocontrol method.Wherein, how the measurement of salt concentration is analyzed with conductivity meter on-line measurement instead of chemical.Experiment shows that as the solution of this type of pot water low concentration, its electrical conductivity and electrolyte content (dissolved solid TDS) roughly are proportionate relationship.In the time of 25 ℃, the pot water conductivity is about 1: 0.6 with the ratio of TDS concentration, i.e. the corresponding 0.6mg/L of 1 μ s/cm.The electrical conductivity temperature influence is very big, take temperature-compensating, and demarcates with chemical analysis results.
About the autocontrol method of blowdown, do not see real continuous control so far.Though have the foreign trader to promote the equipment of continuous blowdown by name in recent years, research shows, all is the intermittent controlled of two formulas without exception: all with conductivity meter monitoring pot water salinity; When electrical conductivity reaches in limited time high; Automatically open blowoff valve, when electrical conductivity drops to a certain lower bound, close blowoff valve.Though this interval-automatic method for discharging pollution improves to some extent than artificial regularly blowdown, salt content fluctuation up and down in high and low limit interval all the time still has certain excessive emissions, is not optimum blowdown control scheme.
Summary of the invention:
Defective to above-mentioned prior art existence; The present invention provides a kind of more energy-conservation method for discharging pollution, adopts the continuous control mode, realize as required, in good time, in right amount, real continuous blowdown; The higher limit that pot water salt content continous-stable is being allowed; Can reduce blowdown flow rate to greatest extent, guarantee the safe operation of boiler, obtain best effects of energy saving and emission reduction.
From mechanism, the rising of pot water salt concentration is caused by steam raising, therefore can pass through steam flow D, extrapolates by following formula and keeps pot needed blowdown flow calculated value of water salinity balance (initial value) W
W＝D×Sg/(Sp-Sg)
In the formula, Sp is that pot water salinity, the Sg that boiler operatiopn allowed is the salt concentration of make-up water.
Say from principle; Can make blowdown flow W follow steam flow D and change automatically, the ratio control system of composition steam flow and blowdown flow by following formula according to the aperture that steam flow D continuously changes blowoff valve; Just can ideally keep the salinity of pot water, realize most economical blowdown.Form such blowdown automatic control system and need dispose steam-flow meter, blowdown flow meter, ratio setting apparatus and continuous actuator (containing executing agency and control valve).The continuous actuator here refers to control valve opening can be by control command from the continuously adjustable actuator of 0-100%, rather than the switch valve that has only " standard-sized sheet " and " complete shut-down " two stable states that uses in the at present interrupted blowdown control system.
But the situation of reality is that the demineralized water salinity Sg that replenishes to boiler changes, and will guarantee that therefore pot water salinity is stable, also needs the salinity of on-line measurement make-up water, revises proportionality coefficient Sg/ (Sp-Sg) at any time.In addition, consider in the boiler operatiopn except that surface blow-off to also have a kind of periodical blowdown to basic sediment, by manual work decision blowing time and blowdown flow rate, obviously, this is the disturbing factor to pot water salinity.This shows; Only press following formula structure open loop ratio control system and can not guarantee that pot water salinity is constant; Also must increase the electrical conductivity close loop control circuit on this basis; Pot water conductivity with real-time measurement is the control target, its electrical conductivity with expectation is compared, by deviation and variation tendency thereof; Automatically revise blowdown flow, to suppress such as the influence of the various disturbing factors such as salinity fluctuation, periodical blowdown and leakage rate variation, steam and blowdown flow instrumentation amount error of make-up water to salinity.For reaching such control effect, the present invention has provided a kind of structure of feedforward and Feedback complex control system.In this system, the output signal of electrical conductivity controller is revised the blowdown flow value automatically through adder calculator, is controlled at pot water salinity all the time on the numerical value of expectation.For reducing investment, the present invention gives a kind of simplified structure of controlling system, is with the original system different character, has saved blowdown flow and has taken into account flow controller B.In this system, when steam flow changed, blowoff valve still can be made quick response, and just the transient error of blowdown flow can increase to some extent, but because the existence of electrical conductivity close loop control circuit is arranged, this dynamic error can rely on electrical conductivity controller A slowly to eliminate.Dynamic error when changing fast for reducing steam flow, the blowdown control valve here require to have working flow characteristic preferably, promptly require to have between blowdown flow and valve position control signal the better linearity relation.
The operating mode that it may be noted that blowoff valve is more special, and it directly enters low-pressure system with pot water by high pressure, and valve two ends pressure reduction is big, temperature is high, is easy to occur the wire drawing corrosion phenomenon, select the special valve of inner multi-step pressure reduction for use.
Description of drawings:
Fig. 1 is that surface blow-off of the present invention is optimized the energy-saving control system schematic diagram;
Fig. 2 is an economical surface blow-off energy-saving control system schematic diagram of the present invention;
The specific embodiment:
The specific embodiment:
Below in conjunction with accompanying drawing the present invention is done and to describe in further detail:
The composition of the surface blow-off optimization energy-saving control system that the present invention proposes is as shown in Figure 1.Be installed in the steam flow signal that the flowmeter on the boiler steam pipe records; After by formula proportionality coefficient multiply by in (1) in the ratio setting apparatus, obtain the blowdown flow initial value of Theoretical Calculation, this initial value is through the command signal of adder calculator (another input signal of supposition is 0 earlier temporarily) output blowdown flow; The actual flow that this command signal and blowdown flow instrumentation get compares; As variant,, change the aperture of blowoff valve then by controller B pushing executing mechanism; Blowdown flow is revised, made the requirement of its coincidence formula (1).The responsiveness of this proportion control is very fast, and except valve event needed slightly the time, the hysteresis of Flow-rate adjustment object was almost nil.
Explain in the superincumbent summary of the invention that to interference such as make-up water conductivity variations and the bottom of a pan periodical blowdowns, above-mentioned open-loop control method is unable to be overcome, and need add the electrical conductivity close loop control circuit in addition.Among Fig. 1, the superficial water of being drawn by drum gets into the conductivity measurement tube, accepts the detection of measurement electrode; The conductivity signal that records is seen off by conductivity meter; The conductivity setpoint that it and boiler require relatively after, in ratio, integration, the differential control algolithm of deviation, export control signal by controller A; Get into adder calculator, increase and decrease additional another input signal (blowdown flow initial value).If the pot water conductivity equals the setting value of requirement, then controller is output as 0, does not promptly revise; If the pot water conductivity is higher than the setting value of requirement, then controller A output＞0, and blowdown flow rate is strengthened; Otherwise then controller A output＜0, and blowdown flow rate is reduced.Rely on the adjustment of controller A, can make pot water conductivity finally be stable at the setting value of requirement initial blowdown flow rate.Such system architecture can be faced various interference, automatically the pot water conductivity is stabilized on the control target of requirement.
What Fig. 2 provided is a kind of structure chart of economical surface blow-off energy-saving control system, and different with Fig. 1 is to have cancelled blowdown flow meter and controller B among Fig. 2, thereby can reduce investment cost.Counterpart is identical among the operation principle of Fig. 2 system and Fig. 1; When steam flow in the system changes; Blowoff valve still can respond fast; But the transient error of blowdown flow can increase to some extent, and this need rely on electrical conductivity controller A through the adder calculator correction, and pot water conductivity is stabilized on the level of expectation.If the steam load changes in flow rate is not too violent, perhaps dynamic error is required not too harshness, this is a kind of scheme of practicality.Certainly, for reducing the dynamic error of electrical conductivity control, preferably select for use to have linear flow characteristic, promptly has the blowoff valve that substantial linear concerns between flow and valve position control signal.
Above content is to combine concrete preferred implementation to further explain that the present invention did; Can not assert that the specific embodiment of the present invention only limits to this; Those of ordinary skill for technical field under the present invention; Under the prerequisite that does not break away from the present invention's design, can also make some simple deduction or replace, all should be regarded as belonging to the present invention and confirm scope of patent protection by claims of being submitted to.
Claims (3)
1. the optimization energy-saving control method of a steam boiler surface blow-off is characterized in that:
(1) steam-flow meter is installed and measures steam flow on boiler steam pipe, the flow signal that records multiply by proportionality coefficient according to following formula in the ratio setting apparatus, obtain the initial set value of blowdown flow
W=D * Sg/ (Sp-Sg)------------formula (1)
In the formula, D is a steam flow, and Sp is the pot water salinity that boiler operatiopn allowed, and Sg is the salinity of make-up water, and W is for keeping pot needed blowdown flow of water salinity balance;
(2) the conductivity measurement tube is set on boiler blow out pipeline, the superficial water that drum is drawn gets into the conductivity measurement tube, measures the top layer electrical conductivity of water through conductivity meter; In controller A; Electrical conductivity that records and the electrical conductivity that pot water allows are compared; And deviation carried out the PID computing, and its output signal is as the correction of blowdown flow, and this correction gets into adder calculator the initial blowdown flow setting value of step (1) gained is increased and decreased correction;
(3) blowdown control valve and blowdown flow meter are set on blow-off line; This blowdown control valve drives with electronic or pneumatic actuator, and executing agency accepts the control of controller B, makes the aperture of blowdown control valve can be adjustable continuously from 0-100% by the order of controller B;
(4) output of adder calculator is delivered to controller B as the control signal of blowdown flow, and controller B also accepts the measuring-signal of blowdown flow meter simultaneously; Controller B carries out the PID computing by deviate after command signal and feedback signal are compared, and again through the action of executing agency, changes the aperture of blowdown control valve, forms the blowdown flow system for tracking, makes actual blowdown flow meet the numerical value that command signal requires;
(5) the above-mentioned FEEDFORWARD CONTROL passage of forming by steam-flow meter and ratio setting apparatus; With the electrical conductivity close loop control circuit of forming by conductivity meter, controller A and blowdown flow system for tracking; Combine through adder calculator, form the feedforward and Feedback complex control system; In such system, the FEEDFORWARD CONTROL passage can provide fast reaction to the variation of boiler capacity, in time changes blowdown flow rate; And the electrical conductivity close loop control circuit to the correction of adder calculator output flow, overcomes interference through controller A, and a pot water salt content is stabilized on the level of expectation.
2. the optimization energy-saving control method of an economical steam boiler surface blow-off, this method is saved blowdown flow meter and controller B, it is characterized in that:
(1) steam-flow meter is installed and measures steam flow on boiler steam pipe, the flow signal that records multiply by proportionality coefficient according to following formula in the ratio setting apparatus, obtain the initial flow setting value of blowdown
W＝D×Sg/(Sp-Sg)
In the formula, D is a steam flow, and Sp is the pot water salinity that boiler operatiopn allowed, and Sg is the salinity of make-up water, and W is for keeping pot needed blowdown flow of water salinity balance;
(2) the conductivity measurement tube is set on the boiler blow-off pipeline; The superficial water that drum is drawn gets into the conductivity measurement tube, measures the top layer electrical conductivity of water through conductivity meter, in controller A; The electrical conductivity that records is compared with the electrical conductivity that boiler operatiopn is allowed; And deviation carried out the PID computing, its output signal is as the flow correction amount, gets into adder calculator the blowdown initial flow setting value of step (1) gained is increased and decreased correction;
(3) the blowdown control valve is set on blow-off line; This blowdown control valve drives with electronic or pneumatic actuator, and executing agency accepts the continuous control of adder calculator, makes the aperture of blowdown control valve can be adjustable continuously from 0-100% by the control command of adder calculator;
(4) in adder calculator, blowdown flow initial set value and the addition of blowdown flow correction value, as the control command of blowdown flow, the aperture through executing agency continuously changes the blowdown control valve changes blowdown flow;
(5) the above-mentioned FEEDFORWARD CONTROL passage of forming by steam-flow meter and ratio setting apparatus; With the electrical conductivity close loop control circuit of forming by conductivity measurement meter, controller A and blowdown actuator; Combine through adder calculator, constitute the feedforward and Feedback complex control system; In such system, the FEEDFORWARD CONTROL passage provides fast reaction to the variation of boiler capacity, in time changes blowdown flow rate; And the electrical conductivity close loop control circuit to adder calculator output flow correction value, is stabilized on the level of expectation a pot water salt content through controller A.
3. energy-saving control method according to claim 1 or claim 2, it is characterized in that: the continuous control mode is taked in said energy-saving control method blowdown, selects the actuator of aperture continuous controllable for use; Under the boiler normal operating condition, the blowdown control valve will stay 3% aperture at least, and letting has running water to flow through in the conductivity measurement tube all the time, makes conductivity meter can reflect the change of water quality in the drum at any time.
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| CN2209762Y (en) * | 1995-03-01 | 1995-10-11 | 高佩斌 | Automatic de-sludging device for boiler |
| JP4551028B2 (en) * | 2001-06-14 | 2010-09-22 | 三菱重工業株式会社 | Nuclear power generation equipment |
| US20030226794A1 (en) * | 2002-06-06 | 2003-12-11 | Coke Alden L. | Steam boiler scale inhibitor, sludge (TSS) and TDS control, and automatic bottom blow-down management system |
| CN2937832Y (en) * | 2006-08-16 | 2007-08-22 | 辽宁省锅炉技术研究所 | On-line water quantity automatic monitoring and blow-down system of steam boiler |
| CN201141591Y (en) * | 2007-12-17 | 2008-10-29 | 中国铝业股份有限公司 | Boiler pollution-discharge capacity-expanding container capable of automatically controlling liquid level |
| JP2009192110A (en) * | 2008-02-13 | 2009-08-27 | Miura Co Ltd | Boiler |
| CN100582580C (en) * | 2008-07-11 | 2010-01-20 | 西安交通大学 | System for implementing grate firing boiler energy saving and discharge reduction by boiler blowdown water |
| CN201382399Y (en) * | 2009-04-30 | 2010-01-13 | 钮德明 | Automatic monitoring device for continuous blowdown of boiler |
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