CN116576457A - A system and method for alleviating the temperature limit of the upper heating surface of a supercritical tangentially fired boiler - Google Patents

Abstract

The present invention provides a system and method for relieving the temperature limit of the upper heating surface of a supercritical tangentially fired boiler. The supercritical tangentially fired boiler includes a furnace and a primary fan. One additional overburning air nozzle, the air inlet of each additional overburning air nozzle is connected to the primary air outlet of the primary fan; the invention can effectively alleviate the problem of lowering the steam temperature on the upper heating surface of the boiler due to irregular metal wall temperature exceeding the limit It greatly improves the safety and economy of boiler operation under low-load operating conditions.

Description

A system for alleviating the temperature limit of the upper heating surface of a supercritical tangentially fired boiler and its method

technical field

The invention relates to the technical field of coal-fired power generation, in particular to a system and method for alleviating the over-limit temperature of the upper heating surface of a supercritical tangential combustion boiler.

Background technique

As the proportion of new energy power generation continues to increase, the low-load operating conditions of traditional coal-fired generating units are gradually increasing. The tangential combustion boilers supporting the supercritical parameter units usually adopt the structure of the burner and the large air box. When the 50% ECR and below low-load operating conditions, the reduction of the air supply volume will directly lead to the pressure drop of the air box, and the rigidity of the secondary air jet will be weakened. The internal combustion structure becomes worse, especially when the SOFA air box in the upper part of the main combustion area is set separately from the large air box in the main combustion area, the jet rigidity of the SOFA air nozzle drops more; at the same time, the steam temperature of the once-through boiler with supercritical parameters is high, and the steam-water parameters change complicatedly 1. The uniform distribution of steam and water parameters is weak, especially the reduction of steam flow rate under low load conditions leads to a decrease in steam flow rate in the tube on the heating surface, and the cooling effect of steam on the tube wall is greatly weakened.

The current boiler combustion system adopts an air-staged low-nitrogen combustion system. Under low-load conditions, the jet rigidity of the secondary air nozzle (main combustion area and SOFA air) of the burner is reduced, the combustion structure is weak, and the center of the flame moves upwards, superimposing the above-mentioned soda System sensitivity and other characteristics, the metal wall temperature of the heating surface (screen over, high over, high over, etc.) in the upper high temperature zone of the furnace is very easy to overheat, and there is no obvious rule to follow in the regular distribution position of the overheating tube panel. During operation, it is often forced to reduce the main and reheat steam parameters to ensure the safe operation of the equipment, which seriously affects the economy and safety of boiler operation.

Contents of the invention

The purpose of the present invention is to provide a system and method for alleviating the over-limit temperature of the upper heating surface wall of a supercritical tangentially fired boiler, which solves the defect of unsafe operation of the boiler caused by the over-limit of the upper heating surface wall temperature of the existing tangentially fired boiler .

In order to achieve the above object, the technical scheme adopted in the present invention is:

The present invention provides a system for alleviating the temperature limit of the upper heating surface of a supercritical tangentially fired boiler. The supercritical tangentially fired boiler includes a furnace and a primary fan. The exhaust air additional nozzle, the air inlet of each said exhaust air additional nozzle is connected to the primary air outlet of the primary fan.

Preferably, the jet flow direction of the additional overburning air nozzle is a counter-type.

Preferably, the arrangement position of the additional overfired air nozzle is the same as the elevation of the SOFA burner.

Preferably, an air preheater is provided between the air inlet of the additional overfired air nozzle and the primary air outlet of the primary fan.

Preferably, the primary hot air outlet of the air preheater is connected to a medium-speed coal mill through a shut-off valve.

Preferably, a regulating valve is provided at the air inlet of the additional overburning air nozzle.

The invention provides a method for relieving the temperature limit of the upper heating surface of a supercritical tangential combustion boiler, comprising the following steps:

On the four walls of the furnace of the supercritical tangential combustion boiler, an additional nozzle for overfired air is arranged;

Under low-load conditions, the excess high-pressure primary hot air enters the overburned air additional nozzle, and the excess high-pressure primary hot air is used to suppress the rising flue gas flow in the furnace.

Compared with the prior art, the present invention has the following beneficial technical effects:

The invention provides a system for alleviating the temperature limit of the upper heating surface of a supercritical tangentially fired boiler. The four walls of the furnace are provided with additional nozzles for overburned air, and then the primary hot air enters the additional nozzles for overburned air. The advantage of high primary air pressure can effectively control the temperature limit of the metal wall on the upper high-temperature heating surface, and also make the unburned components rising in the main combustion zone fully mixed and combusted, improving the economical operation of the boiler; at the same time, the system is simple and the scope of transformation Small and practical.

The invention provides a method for alleviating the temperature limit of the upper heating surface of a supercritical tangentially fired boiler, by introducing hot primary air with a higher wind pressure in the overburning air area under low load conditions, and cooperating with the optimized overburning air additional The setting of the nozzle greatly enhances the rigidity of the jet flow in the area of the overburned air, and simultaneously plays the role of "pressing fire" and "mixing" the rising flue gas flow in the main combustion area, not only suppressing the upper part caused by the irregular rise of the flue gas flow. The overheating of the heating surface and the enhancement of the mixing effect in the burnout zone are beneficial to the burnout of the pulverized coal flow, reducing the carbon content of the fly ash, and improving the safety and economy of the unit operation. It is of great significance to the safe and economical operation of the four-corner tangentially fired boiler with supercritical parameters under low load conditions.

To sum up, the present invention introduces excess hot primary air into the additional nozzles provided in the overburning air area under low-load operating conditions to enhance the jet rigidity of the air in the overburning air area, and to reduce the irregular smoke rising in the main combustion area. The air flow is effectively compressed and mixed, which effectively alleviates the dilemma of lowering the steam temperature due to the irregular and excessive metal wall temperature on the upper heating surface of the boiler, and greatly improves the safety and economy of boiler operation under low-load operating conditions .

Description of drawings

Fig. 1 is the structural representation of the system;

Figure 2 is a schematic diagram of the layout of the medium-speed coal mill;

Figure 3 is a schematic diagram of the position layout of the additional nozzle of the overfired air;

In the figure: 1 is the primary fan, 2 is the blower, 3 is the medium-speed coal mill, 4 is the air preheater, 5 is the main burner, 6 is the SOFA burner, 7 is the additional nozzle of the exhaust air, and 8 is the hot air Regulating valve, 9 are cold air regulating valves, 10 are regulating valves, 11 are cut-off valves, and 12 are boilers.

Detailed ways

The present invention will be further described in detail below in conjunction with specific embodiments, which are explanations of the present invention rather than limitations.

Referring to Fig. 1, the present invention provides a system for alleviating the temperature limit of the upper heating surface of a supercritical tangential combustion boiler, wherein the supercritical tangential combustion boiler includes a furnace 12, a primary fan 1, a blower 2, a medium-speed mill Coal machine 3, main burner 5 and SOFA burner 6, wherein the primary air outlet of the primary fan 1 is connected to the inlet of the air preheater 4, and the primary hot air outlet of the air preheater 4 is connected to the medium-speed coal mill 3 primary wind inlet.

The medium-speed coal mill 3 is provided with a cold air inlet, and the cold air inlet is connected with the primary air outlet of the primary fan 1 .

The secondary air outlet of the blower 2 is connected to the inlet of the air preheater 4, and the secondary hot air outlet of the air preheater 4 is respectively connected to the secondary air of the main burner 5 and the SOFA burner 6 arranged on the furnace 12. import.

The furnace 12 is provided with an additional overburning air nozzle 7 , and the air inlet of the overburning air additional nozzle 7 is connected to the primary hot air outlet of the air preheater 4 .

An additional overfired air nozzle 7 is provided on the four walls at the same level as the SOFA burner on the furnace.

As shown in Fig. 3, the jet direction of the four overburning air additional nozzles 7 is of the opposite type, so as to reduce the rotational momentum of the jets of the overburning air additional nozzles 7 and enhance the penetration of the jets.

The overfired air additional nozzle 7 is provided with one layer.

A regulating valve 10 is provided on the connecting channel between the air inlet of the additional burn-off air nozzle 7 and the primary hot air outlet of the air preheater 4 .

A hot blast regulating valve and a stop valve 11 are sequentially arranged on the connecting channel between the primary hot blast outlet of the air preheater 4 and the medium-speed coal mill 3 .

A cold air regulating valve 9 is provided on the connecting pipe between the cold air inlet of the medium-speed coal mill 3 and the primary air outlet of the primary fan 1 .

The primary air at the outlet of the primary fan 1 is heated by the air preheater 4 and mixed with the temperature-adjusted cold air to enter the medium-speed coal mill 3 to dry and transport coal powder; the secondary air at the outlet of the blower 2 is heated by the air preheater 4 and then enters the main burner 5 and the SOFA burner 6 wind box participate in the combustion in the furnace.

Through the adjustment and control of the regulating valve 10 and the shut-off valve 11, part of the primary hot air can be introduced into the additional burn-out air nozzle 7 arranged in the upper wall of the furnace 12, so as to realize the targeted distribution of boiler combustion air under low-load conditions and effectively control the metal wall. The temperature is frequently exceeded.

As shown in FIG. 2 , the boiler 12 is equipped with multiple medium-speed coal mills 3 , and the number of coal mills put into operation is related to the operating load of the boiler 12 .

Working process of the present invention:

Under low-load conditions, some medium-speed coal mills perform normal pulverization and powder feeding operations, and some medium-speed coal mills 3 are out of service. The cold air regulating valve 9 at the cold air inlet of the outage medium-speed coal mills and the hot air Regulating valve 8 is closed;

The primary air of the primary fan 1 is heated by the air preheater 4, and then the flow is adjusted by the regulating valve 10, and sent to the additional burn-off air nozzle 7 arranged in the wall. The primary air duct is provided with a stop valve 11.

In the actual application process, the wall temperature measurement points that are prone to frequent overheating under low-load conditions in daily operation are selected as monitoring objects, such as the metal wall temperature of the final superheater/reheater and the partition screen and rear screen superheater wall of the furnace roof. During operation under low-load conditions, if the wall temperature of the key monitoring is close to the alarm value set by the operation and continues to rise, then close the hot air regulating valve 8 and the stop valve 11 of the outage coal mill, open the regulating valve 10, and increase The primary blower 1 outputs power to lead the primary air into the overburning air additional nozzle 7, and adjust the opening of the regulating valve 10 in real time according to the monitored metal wall temperature changes on the heating surface until the wall temperature returns to the allowable range.

When there is no over-temperature phenomenon in the wall temperature state of the key monitoring, the regulating valve 10 is closed, and the boiler operates normally in a conventional manner.

The excess high-pressure hot primary air enters the overburning air additional nozzle 7, and at the same time suppresses the rising flue gas flow of the lower furnace, enhances the combustion mixing characteristics of the burnout zone, balances the uniformity of the upward airflow in the burnout zone, and effectively balances the heating surface screen of the upper part of the furnace Over, over, and high re-metal wall temperature distribution, eliminating local over-temperature points, and improving the safety and economy of boiler operation under low-load conditions.

In the prior art, some solutions have been proposed for the overheating of the heating surface of the boiler. For example, the patent CN 111256109 A proposes to divert, expand, and merge the secondary air wind box, burner, and key positions in the exhaust air duct. Optimize and smooth the air flow in the air duct, thereby increasing the secondary air volume in the area near the side wall to alleviate the overheating of the furnace tube wall. However, this scheme is mainly aimed at the opposed boilers arranged on the front and rear walls of the burner. The flue gas flow field in the furnace is relatively uniform. The optimization of diversion, flaring, and confluence of the secondary air distribution in the secondary air box is designed based on high-load conditions. When operating at 50% ECR and below low-load conditions, the air pressure in the secondary air box is significantly reduced. The secondary air volume distribution and flow field characteristics will change significantly, and its effect on metal wall temperature mitigation will be greatly reduced.

Patent CN 113124418 A proposes a method for alleviating the overheating of the local pipe wall on the high-temperature heating surface. By testing and adjusting the highest wall temperature position on the upper part of the furnace corresponding to the powder feeding wind speed of the upstream burner, the method of leveling the primary wind speed of the burner is used to alleviate Corresponding to the over-temperature phenomenon of the upper heating surface, as mentioned above, this method has certain practicability for the opposed combustion boiler with the front and rear walls of the burner arranged at equal intervals. There is an approximate corresponding relationship between the arrangement of the burner along the furnace width and the upper heating surface. Air powder air flow leveling can alleviate the distribution of flue gas field in the upper part of the furnace to a certain extent. However, it is not applicable to the tangential circle boiler with four corners of the burner, and the upper heating surface arrangement of the four corners tangential circle has no approximate corresponding relationship with the lower furnace burner. And the leveling of the primary air powder is generally regarded as the basic condition for the normal operation of the boiler, and its adjustment range is limited and the adjustment hysteresis is relatively large.

The invention breaks through the adjustment method of over-reliance on air classification in the traditional combustion process, and proposes a system that introduces primary air with excess heat to the burn-out air nozzle on the upper part of the boiler under low-load conditions, and reasonably designs and arranges the position and jet flow of the burn-out air additional nozzle Angle, effectively suppress, mix and evenly distribute the irregular flue gas flow rising in the main combustion zone under low load conditions, and realize effective control of the metal wall temperature of the upper heating surface of the furnace.

At the same time, relying on the hot primary air to enhance the jet rigidity in the burn-off air area can effectively avoid the problems caused by the current excessive air classification method, such as high-temperature corrosion of the water wall in the main combustion area, contamination and slagging, and the increase of fly ash combustibles, etc. The safety, economy and environmental protection of the operation are of great significance.

Claims (7)

1. A system for alleviating the supercritical tangential combustion boiler upper heating surface wall temperature overrun, it is characterized in that, described supercritical tangential combustion boiler comprises furnace (12) and primary air blower (1), and wherein, described furnace ( The four walls of 12) are provided with an additional overburning air nozzle (7), and the air inlet of each of the additional overburning air nozzles (7) is connected to the primary air outlet of the primary fan (1). 2. A system for alleviating the over-limit temperature of the upper heating surface of a supercritical tangential combustion boiler according to claim 1, characterized in that, the jet flow direction of the additional overburning air nozzle (7) is a counter-type. 3. A system for alleviating the temperature limit of the upper heating surface of a supercritical tangentially fired boiler according to claim 1, characterized in that the arrangement position of the additional overfire air nozzle (7) is the same as the elevation of the SOFA burner. 4. A system for alleviating the over-limit temperature of the upper heating surface of a supercritical tangential combustion boiler according to claim 1, characterized in that, the air inlet of the additional overburning air nozzle (7) is connected to a primary fan (1) An air preheater (4) is arranged between the primary air outlets. 5. A system for relieving the temperature limit of the upper heating surface of a supercritical tangentially fired boiler according to claim 1, wherein the primary hot air outlet of the air preheater (4) passes through a shut-off valve (11) A medium-speed coal mill is connected. 6. A system for alleviating the overrun of the upper heating surface wall temperature of a supercritical tangentially fired boiler according to claim 1, characterized in that a regulating valve ( 10). 7. A method for alleviating the temperature limit of the upper heating surface of a supercritical tangentially fired boiler, characterized in that it comprises the following steps: An additional overfire air nozzle (7) is arranged on the four walls of the furnace (12) of the supercritical tangentially fired boiler; Under low-load working conditions, excess high-pressure primary hot air enters the overburned air additional nozzle (7), and the excess high-pressure primary hot air is used to suppress the rising flue gas flow in the furnace.