CN109882830B - Operation method for adjusting steam temperature of biomass circulating fluidized bed boiler - Google Patents
Operation method for adjusting steam temperature of biomass circulating fluidized bed boiler Download PDFInfo
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- CN109882830B CN109882830B CN201910066712.6A CN201910066712A CN109882830B CN 109882830 B CN109882830 B CN 109882830B CN 201910066712 A CN201910066712 A CN 201910066712A CN 109882830 B CN109882830 B CN 109882830B
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Abstract
The invention discloses an operation method for adjusting steam temperature of a biomass circulating fluidized bed boiler. The technical scheme adopted by the invention is as follows: reducing the oxygen content of the flue gas to ensure that biomass fuel in the hearth is not completely combusted, and controlling the air quantity entering the material returning device to ensure that combustible gas and combustible soot particles generated by the incomplete combustion of the biomass fuel are combusted again in the material returning device; controlling the difference value between the temperature of the flue gas at the outlet of the hearth, the temperature of the flue gas at the outlet of the feeding back device and the temperature of the ash particles at the bottom of the feeding back device to prevent the feeding back device from coking caused by over severe reburning, controlling the ash discharge speed at the bottom of the feeding back device to assist in adjusting the material level and the bed temperature of the feeding back device, and reburning inside the feeding back device can change the spatial distribution proportion of the combustion heat of the fuel in the boiler and the heat absorption capacity share of each part of the steam heating surface, thereby adjusting the steam temperature of each heating surface. The invention can prevent the metal wall of the medium-high temperature heating surface from overtemperature, reduce the amount of desuperheating water and improve the running economy of the unit.
Description
Technical Field
The invention belongs to the technical field of biomass circulating fluidized bed boilers, and particularly relates to an operation method for adjusting steam temperature of a biomass circulating fluidized bed boiler.
Background
The steam temperature is an important operation parameter of the boiler, the improvement of the steam temperature is beneficial to the improvement of the cycle thermal efficiency of the unit, and the maintenance of the proper steam temperature is an important condition for ensuring the safe operation of the unit. The steam temperature should not be too high or too low, and should meet the design requirements. During the operation of the boiler, the steam temperature must be strictly controlled.
The typical arrangement of the steam heating surface in the biomass circulating fluidized bed boiler is as follows: the medium-high temperature heating surface (medium temperature superheater, high temperature superheater and high temperature reheater) is arranged in the hearth, the low-temperature heating surface (low temperature superheater and low temperature reheater) is arranged in the shaft flue, and the material returning device (comprising a cyclone separator and a material returning device) is arranged between the hearth and the shaft flue. The flue gas flows through a medium-high temperature heating surface and a material returning device in the hearth in sequence and then passes through a low-temperature heating surface in a vertical shaft flue. In the actual operation of the boiler, because the characteristics or the operation parameters of the biomass fuel deviate from the design working condition, the problem that the steam temperature or the metal wall temperature of the medium-high temperature heating surface is easy to generate over-temperature is solved, and the problem that the heat absorption capacity of the steam of the low-temperature heating surface is easy to generate less than the design value is solved. In this case, the conventional regulation method is to inject desuperheating water to lower the steam temperature of the medium-high temperature heated surface. The larger the amount of desuperheating water is, the worse the economic efficiency of the unit is, and the desuperheating water can only reduce the steam temperature of the medium-high temperature heating surface but cannot improve the steam temperature of the low-temperature heating surface. If the heat absorption capacity of the low-temperature heating surface can be improved, and the heat absorption capacity of the medium-high temperature heating surface can be reduced, the metal wall temperature of the medium-high temperature heating surface can be prevented from being over-heated, the temperature reduction water quantity can be reduced, and the running economy of the unit can be improved.
Therefore, how to provide an operation method for adjusting the steam temperature to make up for the limitation of the temperature reduction water adjusting means is a problem to be solved urgently by those skilled in the art.
Disclosure of Invention
In view of the above, the present invention provides an operating method for adjusting steam temperature of a biomass circulating fluidized bed boiler, which utilizes the characteristic that a material returning device of the biomass circulating fluidized bed boiler is arranged between a hearth and a vertical shaft flue, changes the spatial distribution proportion of combustion heat of biomass fuel by controlling the reburning of combustible gas and combustible soot in the material returning device, plays a role of preventing the metal wall temperature of a medium-high temperature heating surface from being over-high, and effectively reduces the amount of reduced temperature water in the process of adjusting steam temperature, so as to improve the operating economy of a unit.
In order to achieve the purpose, the invention provides the following technical scheme: an operating method for adjusting steam temperature of a biomass circulating fluidized bed boiler comprises the following steps: reducing the oxygen content of the flue gas to ensure that biomass fuel in the hearth is not completely combusted, and controlling the air quantity entering the material returning device to ensure that combustible gas and combustible soot particles generated by the incomplete combustion of the biomass fuel are combusted again in the material returning device; controlling the temperature t of the flue gas at the outlet of the furnace1And the outlet flue gas temperature t of the feeding back device2The temperature t of the soot at the bottom of the feeding back device3The difference value prevents the return device from coking caused by too severe reburning, controls the ash discharge speed at the bottom of the return device to perform auxiliary adjustment on the material level and the bed temperature of the return device, and reburning inside the return device changes the spatial distribution proportion of fuel combustion heat in the boiler and the heat absorption capacity share of each part of the steam heating surface, thereby adjusting the steam temperature of each heating surface.
Preferably, the oxygen content of the flue gas does not include the oxygen content in the air which leaks into the flue and does not participate in the combustion reaction.
Preferably, the oxygen content of the flue gas in the straight flue from the flue gas outlet of the feeding back device to the flue gas inlet section of the air preheater is selected as a control object.
Preferably, the amount of air entering the feed back device is regulated by the pressure of the fluidizing air and the pressure of the return air entering the feed back device.
Preferably, when the combustible gas and the combustible soot are combusted again in the feeding back device, the temperature of the soot in the feeding back device and the temperature of the flue gas at the outlet of the feeding back device are increased, and the temperature t of the flue gas at the outlet of the feeding back device is increased by adjusting the oxygen content of the flue gas, the air quantity entering the feeding back device and the ash discharge speed at the bottom of the feeding back device2Specific furnace outlet flue gas temperature t1The temperature is 40-60 ℃, and the temperature t of the ash particles at the bottom of the feeding back device is the same3Is higher than the temperature t of the flue gas entering the feed back device2The height is 10-30 ℃.
Preferably, the bottom of the feeding back device is continuously used for discharging ash, and the ash discharging speed is regulated by a valve or an ash cooling machine.
The invention has the following beneficial effects: the operation method of the invention prevents the metal wall of the medium-high temperature heating surface from being over-heated, effectively reduces the amount of desuperheating water and improves the operation economy of the unit.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a schematic view of a biomass circulating fluidized bed boiler structure, a heating surface and a measuring point arrangement applying the invention;
FIG. 2 is a flow chart of superheated steam of a biomass circulating fluidized bed boiler to which the present invention is applied;
FIG. 3 is a flow chart of reheat steam of a biomass circulating fluidized bed boiler to which the present invention is applied.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides an operation method for adjusting steam temperature of a biomass circulating fluidized bed boiler, which is characterized in that incomplete combustion of biomass fuel in a boiler and reburning of incomplete combustion products in a feed back device are maintained; and controlling the temperature t of the flue gas at the outlet of the hearth1And the outlet flue gas temperature t of the feeding back device2The temperature t of the soot at the bottom of the feeding back device3The difference between the two can prevent the re-burning from causing the back feeding device to coke too violently.
FIG. 1 shows a circulating fluidized bed boiler using biomass according to the present inventionThe structure, the heating surface and the measuring point are schematically arranged, the medium-high temperature heating surface (a medium-temperature superheater, a high-temperature superheater and a high-temperature reheater) is arranged in a hearth, the low-temperature heating surface (a low-temperature superheater and a low-temperature reheater) is arranged in a vertical shaft flue, and the material returning device is arranged between the hearth and the vertical shaft flue. The flue gas flows through a medium-high temperature heating surface and a material returning device in the hearth in sequence and then passes through a low-temperature heating surface in a vertical shaft flue. The boiler operates under the working condition of 130t/h of rated load, the bottom of the feed back device is not continuously ash discharged, the oxygen content of the inlet flue gas of the low-temperature economizer is 7.0 percent, the pressure of the fluidizing air and the pressure of the return air are both 28kPa, and the bed temperature t is4800 ℃, 575 ℃ for flue gas at the outlet of the hearth, 575 ℃ for flue gas at the outlet of the feed back device, 565 ℃ for ash particles at the bottom of the feed back device, and 8.5-9.0kPa for bed pressure. FIG. 2 is a flow chart of superheated steam of a circulating fluidized bed boiler, under the operating condition, the primary desuperheating water flow of a superheater is 4.6t/h, the secondary desuperheating water flow is 3.4t/h, and the temperature of main steam is 540 ℃. FIG. 3 is a flow chart of reheat steam of a circulating fluidized bed boiler, under the above-mentioned operating conditions, the reheater desuperheating water flow is 7.4t/h, and the reheat steam temperature is 548 ℃.
The operation method for adjusting the steam temperature of the biomass circulating fluidized bed boiler under the operation condition of 130t/h comprises the following steps:
1) adjusting the feeding amount to keep the boiler load at 130 t/h;
2) and adjusting the total air volume entering the boiler to reduce the oxygen content of the inlet flue gas of the low-temperature economizer to a range of 2.0-3.5%, and simultaneously keeping the primary air volume to be larger than the critical fluidization air volume. After the oxygen content is reduced, biomass fuel in the hearth is incompletely combusted, and generated combustible gas (mainly carbon monoxide) and combustible ash particles enter a feed back device along with flue gas.
3) Increasing the pressure of the fluidized air and the pressure of the return air, increasing the amount of air entering the return device, burning the combustible gas and the combustible ash particles in the return device again, and monitoring the ash particles t at the bottom of the return device3Rising to 650 ℃, and returning the outlet flue gas temperature t of the material device2Rising the temperature to 630 ℃, and the temperature t of the ash particles at the bottom of the feeding back device3Outlet of specific material returning deviceTemperature t of flue gas2The temperature is 20 ℃ higher, and the pressure of the fluidizing air and the pressure of the return air are 33 kPa.
4) The bottom of the material returning device is started to discharge ash, the ash discharge speed is controlled by the rotating speed of the ash cooling machine, the amount of the cold ash returning to the hearth is reduced, and the bed temperature t is enabled to be4Increasing to 820 ℃. Monitoring the temperature t of the flue gas at the outlet of the furnace1The temperature is increased to 580 ℃, and the temperature t of the flue gas at the outlet of the feed back device is increased2Specific furnace outlet flue gas temperature t1The height is 50 ℃.
5) Slag is discharged from the bottom of the hearth at regular time, so that the bed pressure is still maintained at 8.5-9.0 kPa.
6) And regulating the primary desuperheating water flow and the secondary desuperheating water flow of the superheater to stabilize the temperature of the main steam at 540 ℃, wherein the primary desuperheating water flow is 5.0t/h, the secondary desuperheating water flow is 1.0t/h, and the total flow of the desuperheating water of the superheater is 6.0 t/h.
7) And adjusting the reheater desuperheating water to stabilize the temperature of the reheated steam at 540 ℃, wherein the flow rate of the reheater desuperheating water is 5.2 t/h.
By adopting the operation method, the temperature of the main steam and the temperature of the reheated steam of the boiler can be stably maintained at 540 ℃, the flow of the desuperheating water of the superheater is reduced by 2.0t/h, the desuperheating water of the reheater is reduced by 2.2t/h, and no coking exists in the feed back device.
Claims (5)
1. An operation method for adjusting steam temperature of a biomass circulating fluidized bed boiler is characterized by comprising the following steps:
reducing the oxygen content of the flue gas to ensure that biomass fuel in the hearth is not completely combusted, and controlling the air quantity entering the material returning device to ensure that combustible gas and combustible soot particles generated by the incomplete combustion of the biomass fuel are combusted again in the material returning device;
controlling the temperature t of the flue gas at the outlet of the furnace1And the outlet flue gas temperature t of the feeding back device2The temperature t of the soot at the bottom of the feeding back device3The difference value between the temperature difference value and the temperature difference value prevents the re-burning which is too violent to cause the coking of the material returning device, the ash discharge speed at the bottom of the material returning device is controlled to carry out auxiliary regulation on the material level and the bed temperature of the material returning device, and the re-burning in the material returning device changes the spatial distribution ratio of the fuel combustion heat in the boilerAdjusting the heat absorption capacity of each part of the steam heating surface, thereby adjusting the steam temperature of each heating surface;
when combustible gas and combustible soot are combusted again in the feeding back device, the temperature of the soot in the feeding back device and the temperature of flue gas at the outlet of the feeding back device are increased, and the temperature t of the flue gas at the outlet of the feeding back device is increased by adjusting the oxygen content of the flue gas, the air quantity entering the feeding back device and the ash discharge speed at the bottom of the feeding back device2Specific furnace outlet flue gas temperature t1The temperature is 40-60 ℃, and the temperature t of the ash particles at the bottom of the feeding back device is the same3Is higher than the temperature t of the flue gas entering the feed back device2The height is 10-30 ℃.
2. The operating method for adjusting the steam temperature of the biomass circulating fluidized bed boiler according to claim 1, wherein the oxygen content of the flue gas does not contain the oxygen content of air which leaks into the flue and does not participate in the combustion reaction.
3. The operating method for adjusting the steam temperature of the biomass circulating fluidized bed boiler according to claim 1, wherein the oxygen content of the flue gas in the straight flue from the flue gas outlet of the feeding back device to the flue gas inlet section of the air preheater is selected as a control object.
4. The operating method for adjusting the steam temperature of the biomass circulating fluidized bed boiler according to claim 1, wherein the amount of air entering the feeding back device is adjusted by the pressure of the fluidizing air and the pressure of the return air entering the feeding back device.
5. The operating method for adjusting the steam temperature of the biomass circulating fluidized bed boiler according to claim 1, wherein the bottom of the feeding back device continuously discharges ash, and the ash discharging speed is adjusted by a valve or an ash cooler.
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| US5237963A (en) * | 1992-05-04 | 1993-08-24 | Foster Wheeler Energy Corporation | System and method for two-stage combustion in a fluidized bed reactor |
| CN101709869B (en) * | 2009-12-18 | 2011-09-07 | 杭州电子科技大学 | Hybrid control method for superheat steam temperature system of coal-fired boiler |
| CN102095195B (en) * | 2011-01-11 | 2013-04-17 | 清华大学 | Reburning type circulating fluidized bed boiler |
| CN102384469B (en) * | 2011-07-14 | 2013-08-14 | 清华大学 | Oxygen-controlled fluid bed system and operational method thereof |
| CN102537943B (en) * | 2012-01-17 | 2014-04-02 | 清华大学 | Horizontal type circulating fluidized bed boiler with horizontal cyclone separator |
| CN105805739B (en) * | 2014-08-29 | 2019-07-23 | 中国科学院工程热物理研究所 | Adjust the circulating fluidized bed combustion method of superheat steam temperature |
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