Questions&Answers

In recent years, with the rapid development of iron and steel industry, energy recycling and reducing energy loss has become an important task in the current production and operation of steel companies. With the change of production mode, a large amount of coke oven gas surplus appears, in order to fully digest the coke oven gas surplus, the original method is to mix the coke oven gas directly into the main blast furnace gas network for users. After the actual operation, it is found that, due to the high and coke oven gas mixing amount according to the amount, the change is frequent and the range is large, the fuel calorific value of the furnace is not stable, causing the boiler overpressure, the safety valve frequently jump, not only damage the boiler pressure parts, and the subsequent stable operation of the steam turbine blower, generator has brought adverse effects. In addition, all three blast furnace blowers of Xuangang adopt turbo-blower, and are not equipped with electric towing blower. If the blast furnace gas is interrupted under extreme circumstances, all boilers in line will not be able to provide normal steam for the blower, which seriously threatens the overall production of the company.

Retrofit of burner

The boiler originally had 4 layers of 16 blast furnace gas burners, the first and fourth layers of burners were replaced by coke oven gas burners after the transformation. There were 8 burners in two layers, and the gas pipe, corresponding valve instrument accessories, ignition device, local control box and other accessories were replaced accordingly. The second and third layers of blast furnace gas burners were old.

Modification of heating surface

For coke oven gas calorific value is higher, coke oven gas boiler heating surface need less, the existing boiler heating surface is relatively big, will lead to the following conditions: (1) due to the chamber of a stove or furnace heating surface is too big, lead to a stove or furnace outlet flue gas temperature is reduced, superheater heat decreases, superheater steam temperature is lower than the original, can not reach the rated temperature, especially in low load condition is more serious, need to increase the superheater in the heated area. (2) Due to the large sulfur and water content in coke oven gas, too low exhaust temperature will cause serious low-temperature corrosion to the heating surface of the tail. Therefore, it is necessary to reduce the heating surface of the tail coal economizer and increase the exhaust temperature.

Reconnect the gas line

DN800 main pipe of coke oven gas shall be set up from the main network of the north ring of coke oven gas to boiler No. 5, butterfly valve, blind plate valve and corresponding metering device shall be installed, and branch pipe, four-angle pipeline and regulating valve shall be installed according to the design requirements of burner.

The practical application of converting bf gas boiler to coke oven gas has effectively alleviated the limitation of industrial boilers which use BF gas as the main fuel in the process of production adjustment and realized the effective utilization of coke oven gas. With the increasing competition in the steel market, it is an effective way to reduce cost and increase efficiency for iron and steel enterprises to use gas rationally, reduce external emissions and convert surplus gas into electric energy. The practical application of this technology has a good prospect of promotion.

There is a problem

1.Fan underload

Due to the recirculation of flue gas into the fan inlet, the volume of fresh air from the fan is reduced, which cannot provide the air volume required for boiler steam generation at 75t/h.

2.Condensation water causes corrosion

Because the high temperature smoke is mixed into the fresh air, there are more condensate water at the entrance of the backup fan and the low discharge point, which causes corrosion to the smoke duct and fan.

3.Self - operated gas relief valve can not adapt to the working condition well

For many times, the gas flow rate has been greatly reduced due to the freezing and condensation of the guide pipe of the self-operated gas pressure reducing valve, which endangers the normal production of the boiler. Also appears a pressure relief valve core adhesion, the valve can not adjust the pressure phenomenon.

4.No spare gas filter

There is no parallel backup or bypass line for the gas filter. In case of blockage or other faults, it will not be able to provide fuel for the boiler normally, which will lead to the shutdown of the boiler.

5.The water wall pipe was damaged during the removal of the flame guard belt

The demolition of the fireproof belt was done by artificial percussion drilling, which caused many impact pits on the water-wall pipe. After the demolition work is completed, the repair welding is carried out. But it does pose a long-term risk.

Optimization Suggestions

1.Add row setting

Set discharge is added at fan inlet and low point of pipeline to discharge the condensate water and reduce it.Corrosion, avoid condensation water on the fan operation to produce adverse effects, avoid condensation water with the wind.Go into the burner. At the same time, it should be noted that the condensation water with welding slag and other impurities, need to pay attention.Drain to prevent impurities from blocking the drain line.

2.Redesign of self - propelled gas relief valve

Because the gas in the refinery is easy to have trace amount of coke powder, it is suggested to select the pressure reducing valve that can adapt to the working condition, so as to create good conditions for the boiler's long period stable operation. At the same time, in the process of gas treatment should also strengthen the quality control, avoid the phenomenon of gas with coke powder.

3.A parallel gas filter is added

When there are problems with the filter, switch to another set of filter for operation, and disassemble and clean the blocked filter to ensure the continuous operation of the boiler.

4.Replace part of the water wall pipe in the flame retardant zone

In order to eliminate the impact pit caused by the water wall pipe in the construction process and the bad influence of repair welding in the later period, it is suggested to replace this part of the pipe section by selecting a machine.

5.Make special care plan for boiler operation during renovation

The construction and renovation will take one month. During this period, the boiler cannot be used for backup. If the boiler in operation is abnormal, it will have a huge impact on the steam supply of the whole refinery. Need to make the special care plan of the running boiler.

Cause analysis of boiler coking

1.Component damage causes coking

The degree of boiler rotation is related to the combustion airflow, but the experiment shows that the optimal combustion airflow is open airflow. However, the design of the burner is unreasonable and the adaptability of coal ash is poor. When the nozzle of the burner and the concentration distributor of the combustion chamber or pulverized coal are damaged, when the rigidity of the primary wind speed is reduced, resulting in shorter gas flow range, the occurrence of this phenomenon causes the destruction of the normal airflow required by the burner, and the formation of the fully diffused airflow. However, when the air flow leaves the burner, it expands and moves along the combustion wall, which, on the one hand, will lead to local temperature rise of the burner and, on the other hand, will lead to flame brush wall or combustion deflection.

2.Oxygen content

The oxygen content has a great relationship with the smoke temperature at the exit of the boiler furnace. When the oxygen concentration is low, the combustion effect of pulverized coal will be reduced, the burnout time of pulverized coal will be prolonged, and the flame center point will be moved up. The underburned part will be reburned as the airflow reaches the upper burnout area of the furnace. Because the non-rongfen part will burn in the burning-out zone, resulting in a significant increase in the temperature of the burning-out zone. With the reduction of oxygen content and the increase of load, the smoke temperature at the furnace outlet will significantly increase, thus causing coking. Therefore, the content of oxygen has a very big influence on the coking phenomenon of boiler.

3.Wind speed too fast

In general, the designed wind speed of the combustion nozzle of the boiler is 27m /s, and the wind speed of the air pipe is 29m /s. By measuring the inlet wind speed of the coal mill, it is found that the actual wind speed cannot be exactly the same as the designed value, thus leading to the outlet speed of the coal mill pipeline is 25m /s. In this way, the wind speed is 4 m/s lower than the design value, which leads to the increase of the flue gas return flow of the burner, causing the combustion in advance, and thus causing coking. Therefore, the wind speed should be monitored in real time to adjust the wind speed in time to avoid coking.

Improvement measures for boiler coking

1.Design overhaul

When the burner, heating surface and other factors that affect the power in the furnace are reformed, the design coal type and actual ratio shall be taken into comprehensive consideration, and the data analysis and calculation shall be carried out. The design scheme shall be improved through data analysis and calculation, so as to ensure the comprehensive adaptability of the boiler to different types of coal charcoal. When the design of the burner is improved, the boiler should be aerodynamic field test before use, check the installation Angle of the burner, and determine whether the boiler power field meets the design requirements and use requirements. At the same time, the central support components of the burner and nozzle castable and other numerical evaluation, and timely inspection and maintenance of the boiler unit, damaged members to replace or repair.

2.Reduce the swirl strength of the burner

In the process of combustion test, mainly to the nitrogen dioxide burner to consider, study the generation and stability, through contrast experiment analysis, in the process of burning hedge swirl burner not only to consider the stability of nitrogen dioxide and generation, should also be flammability of pulverized coal, the wastage of the burner, burning zone coking phenomenon such as comprehensive consideration. According to the actual situation, adjust the air volume at the position of 100mm to get the best effect.

3.Coal blending

When matching with combustion materials, coal types should be controlled. If mixing with melting point crossover or easy coking varieties, the boiler should be checked constantly. If the boiler has coking phenomenon, the ratio should be adjusted timely, and after cleaning the furnace, it should be mixed again according to the new ratio. In the allocation of pulverized coal proportion, the characteristics of various pulverized coal shall be fully considered, the proportion of pulverized coal shall be reasonably allocated, the proportion shall be timely adjusted according to the actual situation, the way of stratified combustion in the boiler shall be carried out to avoid boiler re-coking.

Determine the exact number of burners

In the actual transformation of the construction unit, to avoid the simultaneous operation of multiple gas burners serial explosions due to a fault burner, we suggest that the number of gas burners be controlled below 4. In addition, we suggest to add an oil gun inside the gas burner to adapt to the low-load operation of the boiler, and then install a set of furnace chamber flameout explosion-proof equipment, to avoid the boiler under the low-load extinguish and temper the problem.

Arrange the burner layout

The best arrangement of the gas burner is to ensure that the flame in the furnace chamber is in the geometric center of the whole furnace. The traditional technology makes the coal-fired boiler, the general furnace depth is larger, in order to ensure the low temperature operation of the front smoke box, the burner will usually be arranged on the front wall of the furnace. At present, the common small and medium-sized coal-fired boilers are divided into two types: layer combustion mode and chamber combustion mode. Common layer-type boilers such as chain furnaces, layer-type boilers are characterized by the ability to maintain combustion in a fixed or slow-moving chamber. During the transformation of the chain furnace, the shape of the front and rear walls and the shape of the boiler make the installation of the burner difficult. We can install the gas burner on the side of the chain furnace. The goal of the transformation is to make the heat exchange condition in the boiler reach or even better than the condition before the transformation. The gas burner should be installed in the lower position of the center of the sidewall of the furnace. When reforming another pulverized coal furnace, the construction personnel can use the original position of the nozzle of the pulverized coal burner to install the new burner and reduce the amount of reconstruction work as far as possible.

Design the matching of furnace layout

Having selected the type and position of the gas burner, we should also calculate the match of the furnace. Above all, want to smoke exhaust volume calculation, smoke exhaust quantity need matching with induced draft fan, coal boiler is usually calculated according to the generated in coal combustion flue gas of coal smoke exhaust volume of induced draft fan for boiler, gas boiler renovation, because of the smoke density and flow has changed, so need to match the induced draft fan, difficult to avoid gas in the boiler ignition and flue gas emission temperature too high. Secondly, it is necessary to test whether the amount of air in the furnace air leakage system and the gas burner matches.

Select boiler explosion-proof measures

After the coal-burning boiler is transformed into gas-fired boiler, the construction party should take necessary safety protection measures for the users, such as automatic ignition device, quick cut-off valve, flame monitoring system and other protection measures. Develop strict safe operation guidelines for users and supervise their implementation, especially for purge during ignition start. When the boiler works, adjust the proportion of air, prevent flameout, tempering and other problems, to ensure the complete combustion of gas.

First, the main burner was transported to 0 m of the boiler using a flat transport vehicle, and the burner was lifted to the towing chute arranged on the 39.2 m of the boiler by a 300 ton truck crane. In the process of towing the burner, 2 5-ton backchain units are used to drag the burner to the boiler center.

When the upper end of the burner reaches the bottom of the pulley group, use 60.5 mm of the wire rope four as the pulley group hoisting rope, using a 10-ton winch main crane. During hoisting, two 10-ton inverted chains are dragged to the outside of the boiler during the lifting of the burner to prevent the burner from rising too fast until the burner is completely upright. Before the burner is hoisted, another 20-ton hand hoist is equipped to adjust the levelness of the main burner. No force will be put on the chain before the 20-ton burner is hoisted. After the burner is raised, make the hand hoist bear force and adjust the burner level.

During the hoisting process, the rooting beam, pulley block, wire rope and burner must be monitored by someone and equipped with intercom to keep the communication unobstructed. In the process of vertical lifting, due to the narrow space on the upper part of the burner, a hand hoist should be hung at the lifting lug to make the burner move as far as possible between the water cooling wall and the steel structure platform during vertical lifting. During the lifting process, the commanding personnel will direct the main winch to lift, assign special personnel to monitor each dangerous position, and set up the burner smoothly. When the burner is fully upright, it should be suspended at 100mm above the ground and checked everywhere, especially the rooting area. Lifting should be allowed only when there is no problem. The lifting process should be kept slow and smooth.

Remove the 5 ton chain drag after the burner is fully upright. The conductor directs the hoist to drop the hook slowly, and in the process of falling the hook, a monitor is arranged at each floor platform and coal pipeline to monitor the burner during its descent. The Angle and position of the burner can be adjusted at any time during the lifting and descending of the burner by using a rope to prevent the burner from scraping against the surrounding steel beams and pipes.

When the equipment rises to the installation position, 2 10-ton hand hoist and pulley blocks are used to adjust the position of the burner, so that the burner is in place. Using the internal lifting platform of the sprayer, 4 10 tons and 4 5 tons hand hoist, adjust the burner to the required position.

The center line of furnace is drawn out with steel wire, and the intersection point of the two steel wires is the center point of boiler. Draw the imaginary circle on the board and nail the corresponding cutting points to fix the steel wire; The horizontal pipe is used to find the plane elevation of the board (with imaginary tangential circle), so that it is consistent with the central elevation of the nozzle, and the center of the imaginary tangential circle coincides with the central point of the boiler. Hold the plank in place. Based on the vertical end face of each layer of pulverized coal nozzles of each burner, the verticality of the burner was finally rectified by using steel ruler, line drop and hand hoist. A straight line is drawn from the center point of the corresponding nozzle to the imaginary tangent point with steel wire. Adjust the burner so that the center line of the nozzle coincides with the theoretical tangent.

After passing the adjustment and acceptance, the burner is firmly connected with the nearby steel frame. After passing the reexamination of the dimensions, the water-cooled wall is sealed and connected with each rigid beam.

After welding and adjustment of the burner, lift the SOFA burner to the 39.2m layer beam according to the hoisting mode of the main burner. Use two 5-ton chain downlink drags to the installation position, hoist the SOFA burner into place and align it in the same way.

In the process of aligning the main burner and SOFA burner, the lifting platform is used internally to align the joint, and scaffolding is set up externally to align the joint. After the burner is in position and aligned, the hook is not allowed to be removed from the winch before the water-wall connection and the burner fixation device have not reached the required strength. After the burner is installed in place, install the coal gate, each layer of coal pipe elbow, corner seal hood. Remove temporary reinforcement and cut burner temporary beam.

After the high-altitude demolition of the four-angle burners, the method of lifting first and then horizontal transportation is adopted, and then the mobile crane is used to lift them from the outside of the furnace, so as to minimize the workload of the demolition and recovery of relevant equipment, reduce the impact on other work under the furnace, and shorten the time limit for completing the transformation of low-nitrogen burners for large thermal power units.

1. Boiler check calculation

The boiler accounting work must be carried out when carrying out the low nitrogen transformation. The specific needs include the following contents: the balance accounting between the boiler combustion system and the soda water system; The momentum of the boiler dynamic field and the influence index of the transformation process on the dynamic state of the burner. In short, it is necessary to reduce nitrous oxide emissions and maintain the boiler in an optimal stable state under the premise of completing the system transformation.

2. Burner modification and installation

Before the installation of the burner, some preparatory work is essential. First, the control of the horizontal Angle of the burner should be strictly horizontal, the size of deflection Angle should be precisely measured, and the verification work should be completed. The determination of the nozzle size and the diameter of the tangential circle should be carried out in accordance with the standards to ensure that the design standards are met.

3. Cold state acceptance of burner modification

In the renovation of cold state acceptance, it is necessary to balance the circumferential acceptance of the burner, and it is also very necessary to calibrate and balance the wind speed, and the best value should be determined through strict experiments.

4. Optimization and adjustment of combustion after modification of low-nitrogen burner

It is necessary to modify the original combustion mode after the low-nitrogen transformation of the burner to ensure that the adjusted scheme can meet the safety requirements and meet the relevant low-carbon emission standards. The specific is to control the nitrogen emissions in the safe concentration index.

1) Operation mode of burner. For the transformation of low nitrogen burners, the focus should be placed on how to enhance the temperature of the furnace and the stability of pulverized coal combustion, so as to avoid the sudden shutdown or insufficient power of the burner as far as possible.

2) Boiler secondary air distribution mode. The secondary air distribution mode of the boiler should meet certain basic needs to ensure that the surplus air coefficient in the main combustion area is within a reasonable range; When the burner needs to be out of service, the damper corresponding to it should be properly closed; After the completion of the first reconstruction project, the opening and closing degree of the damper is determined by its corresponding flow curve. In the process of boiler operation, it is necessary to ensure that the air pressure of the bellows is normal, which can meet the rigid demand of the air jet.

3) Boiler operating oxygen. To control the oxygen content of the boiler in a reasonable range, it is necessary to determine the optimal oxygen content of the boiler in combustion according to the actual combustion test results.

5. Strengthen the coal blending and blending management after the transformation of low nitrogen burner

It is one of the key contents of the management to strengthen the coal blending and blending management of the boiler after the transformation of low nitrogen burners. It has special assessment standards, so it is strictly prohibited to buy residual mixed cinders in theory. The corresponding coal matching needs need to adopt the opinions of coal source suppliers. Once there is an abnormal phenomenon, it is necessary to make timely response and urgently formulate solutions. In the mixing process of coal burning, it is necessary to pay special attention to the effect of slagging on boiler performance.

The functions and characteristics of PLC control system

(1) For the combustion system of calcining rotary kiln, the size and proportion of the primary damper can be automatically controlled according to the hot air temperature from the furnace; Adjusting the valve and valve simultaneously with coarse adjustment and fine adjustment can avoid the temperature oscillation during the adjustment process.

(2) Equipped with hot/cold starting switch and local/remote ignition functions to adapt to various working conditions.

(3) With hand/self-moving optional on/off. When manual mode is adopted, each execution unit can be started and stopped manually on the control cabinet, and the control valve, small fire gas electric control valve and electric damper can be separately controlled, so as to meet the requirement of manual control of temperature rise during drying kiln.

(4) Purge before ignition and purge after flameout can be realized automatically for each startup or shutdown to ensure safety.

(5) With system safety interlocking protection function. When the gas pressure is ultra-low, the wind pressure is ultra-low, or the induced draft fan stops, or when the gas leakage occurs on site or the burner shuts off, sound and light shall be sent to alarm, and the fuel shall be cut off immediately and the primary and secondary fans shall be kept for purging. There is a special emergency stop button, when pressed immediately cut off the fuel. When the secondary air pressure is very low, sound and light alarm will be issued without stopping.

(6) During the working process of the burner, when the control system detects any conditions that do not meet the requirements of safe combustion, it will immediately conduct safety linkage, cut off the natural gas and purge. The next ignition can only be carried out after troubleshooting.

(7) the DCS control system and the upper machine communication is to rely on up a machine with dry contact and analog signals, including the flameout, low wind pressure, low gas pressure, ignition flame failure, small fire flame, scavenging before and after the scavenging furnace with embers and other rotary kiln parameter overrun, combustion chamber overtemperature switch quantity, and natural gas, air pressure, flow rate signal, analog signals such as the opening of the valve position.

(8) The control loop has a separate manual control function. In case of PLC failure, the burner can also be manually controlled.

First,Boiler combustion transformation of thermal power plant

At present, China's technology and technology cannot achieve the full realization of nuclear power generation, so its main power generation mode is still thermal power plants. In order to solve its environmental pollution problem, it is necessary to apply the low-nitrogen combustion transformation technology accordingly, so that China's thermal power plants power generation on the road of sustainable development. The core of its low-nitrification combustion transformation is to upgrade the traditional combustion mode to the three-dimensional graded combustion mode by using the vertical pulverized coal super-concentration separation technology. In the actual transformation process, the burner in the original boiler needs to be re-improved and rearranged to be a low-nitrogen burner in an overall way, and its pulverized coal nozzles should be changed to an up-down swinging structure and separated vertically to achieve the purpose of improving the heat efficiency of the low-nitrogen burner and reducing NOx emission.

Second, low nitrogen combustion operation optimization of thermal power plant.

After replacing the traditional burner with a low-nitrogen burner, it is necessary to carry out corresponding optimization work, so as to ensure the normal operation of the boiler comprehensively and improve the power generation rate, expand the economic benefits of the thermal power plant, and reduce the gap between steam temperature and smoke temperature on both sides. At present, the commonly used operation optimization measures for low nitrogen combustion in thermal power plants can be roughly divided into adjusting pendulum Angle and burnout wind. Adjust the primary wind, secondary wind and boundary wind; Adjust the oxygen in the furnace; Adjust a few measures such as pulverized coal fineness.

Adjusting the pendulum Angle and burning-out air means that under the condition of high steam temperature, appropriately reducing the burner's pendulum Angle and optimizing the burning-out air can effectively reduce the oxygen content, appropriately increase the upper combustion rate, and significantly improve its low-nitrogen combustion efficiency.

Adjustment of primary air, secondary air and perimeter wind refers to the realization of low oxygen combustion in the main combustion area through the realization of secondary air combination, and the actual adjustment of corresponding parameters, and the more suitable adjustment of secondary air through the actual low-nitrogen combustion situation.

Adjusting the oxygen content in the furnace refers to controlling the oxygen content in the furnace between 2.5% and 3.5%, which can obviously reduce NOx emission and ensure that the boiler can maintain a good working efficiency for a long time.

To adjust the fineness of coal powder is to adjust the separator baffle appropriately, make it smaller, reduce the fineness of coal powder, and finally make the combustion of coal powder more sufficient, which can effectively prevent the overheating of the heating surface due to the low oxygen environment, and improve the safety and stability of its boiler operation.

Cause analysis

(1) The head of the lamp is located outside of the center air gun. Because of the high load of the center air gun, the head of the lamp is in the high temperature area, so the welding seam of the head of the lamp on the lamp is aged, leading to the flame burning from the weld and burning out the head of the lamp.

(2) The burner now in use was designed and manufactured according to the environmental requirements at that time. The central air gun is arranged in the central position of the burner, and the burner itself is composed of a burning path made up of brazing brick and fire path brick, and a burning flame is formed in the burning path.

(3) Due to the high hydrogen content in the fuel (61%), the flame burns faster, so the flame temperature in the central area of the firebrick is very high. Due to the damage or non-solid insulation lining between the firebrick installation and the furnace bottom, the temperature of the firebrick radiates to the furnace,the bottom plate and the upper cylinder of the burner cause the overtemperature of the burner housing.

(4) In the high temperature region at the center of the burner, local high temperature causes N2 and O2 in the air to react to produce a large amount of NOx (NO, NO2); In the fuel gas, the hydrogen content is too high (more than 20%), resulting in the fuel combustion speed is too fast, the flame center temperature is high, so a large amount of NOx is formed, resulting in the flue gas emission cannot meet the emission standards.

The measure

1. Adjustment of burner head size, height and load distribution

Combined with the change of fuel gas composition, the nozzle size of the center gun and side gun of the burner can be changed to reduce the load of the center gun by 20% and reduce the flame height. Adjust the nozzle size of edge gun, so as to adapt to the composition change of fresh air to a certain extent.

2. Burner head coking, partial flame burning, furnace temperature uneven

During the process of fuel gas entering the burner nozzle, affected by the high temperature flame of the surrounding main burner, it may be heated to carbonization and coking inside the burner under the nozzle, gradually causing partial flame burning and uneven furnace temperature. In view of this operation situation, the fuel gas composition should be adjusted, and the fuel gas should be separated from liquid in advance. The gas-liquid separator should be set with liquid level meter to drain out the liquid in time when the liquid phase is generated, so as to prevent the fuel gas from taking liquid.

3. Overtemperature of outer wall of burner

In order to solve the overtemperature phenomenon of the outer wall of the concentrated flame burner, the innovative modification of increasing the height of the small brazier in the central gun of the burner, improving the flame core, reducing heat radiation and avoiding excessive heat radiation to the outer wall of the burner was adopted.

4. The NOx content in the flue gas after combustion exceeds the standard

Adopt graded combustion (multi-gun structure), inside and outside two layer side air gun; Flue gas recycling technology, the change in burner burner brick structure form, will be cut between high ever-burning lamps only design auxiliary air rifle gun and level, the main gun out from the edge of the burner brick, implements the fuel gas classification and by introducing a relatively low temperature of flue gas spray hole high-speed, the burner flame cutting into high area, avoid the generation of high temperature, will be independent of its center point changes to eight small spear, point size by phi 80 changed to phi 34, into the wind form changed to ring into the wind, the evenness of fuel gas and air mixture. Fuel fractional combustion technology arranges fuel gas nozzles in a stepped shape. All the burning air is injected into the center of the burner and passes through the stepped fuel gas nozzles in turn to form several burning areas. Above the nozzle with the lowest position is the primary combustion area. The primary fuel gas is completely burned under the condition of a large amount of excess air, the temperature is not easy to rise, and the nitrogen oxide generated is reduced. The secondary fuel gas nozzle is usually arranged on the outside of the burner brick, and the secondary fuel is injected into the mixed flue gas from the upstream. High speed injection of secondary fuel gas can produce a low pressure zone, will be the furnace in cold sinking of oxygen poor smoke inhalation combustion zone to participate in the combustion, which not only reduces the flame temperature, but also can reduce the oxygen concentration in the combustion zone, thus reducing NOx generation.

Data processing in a power generation system

By intelligently testing and verifying the data generated by the power generation system, optimizing the boiler combustion regulation system has shown the potential to save millions of dollars in fuel costs per year. The thermal power plant data 800 MW rated combustion units are equipped with intelligent control and regulation systems to improve fuel economy. By implementing the boiler burner management system for data processing, power plants can save millions of yuan in costs during the boiler's operating life. The system based on intelligent control can improve combustion efficiency and reduce fuel consumption and cost. The data processing in the power generation system comes from the large amount of real-time data generated during the operation of the boiler and generator. The intelligent control of analyzing and acting on the large amount of data is beyond the capability of operators. An intelligent control electronic system is designed to manage and control the boiler combustion process, reducing deficiencies in manual intervention. Boiler burner automation technologies have been operating for decades, but they still cannot handle the operational data levels generated by combustion systems. However, intelligent control can overcome the challenge of massive data and create an optimized boiler combustion regulation system. How data variables affect boiler output, such as low calorific value, intelligent control must be adapted to maintain the limit level and improve combustion efficiency. Because maintenance, instrument calibration, and fuel change status are ongoing, operators do not work well. The adaptive characteristics of intelligent control systems enable them to deal more effectively with real-time changes in physical parameters such as temperature, fuel supply rate and intake damper position. A change in fuel supply will change the intake damper position almost instantaneously, intelligently adjusting the correct damper position to compensate for the change in fuel supply.

Boiler combustion pollution control

Boiler combustion is itself a polluting process, and environmental laws strictly limit the concentrations of sulfur dioxide, nitrogen oxide and PM2.5 that are released into the atmosphere, and have become increasingly stringent with the development of society. Intelligent control can effectively improve existing boiler designs and pollution reduction technologies, enabling plants to provide heat or electricity at a reasonable cost while complying with environmental regulations. Intelligent control of pollution from coal-fired boilers can be applied at all stages of the combustion process. The choice of fuel for boiler combustion is the first step in reducing flue gas pollutants. For example, natural gas combustion is cleaner than fuel oil, medical waste or biomass and produces the least amount of pollutants in its flue gas. Most domestic boilers cannot choose fuel, and the intelligent control system can adjust the fuel and air volume ratio of each layer of burners according to the industrial analysis of the fuel into the furnace, so as to reduce pollution. Intelligent control of boiler combustion can also reduce the production of nitrogen oxides, the boiler fuel from ignition to burnout each process can be calculated and data analysis to give the most reasonable air ratio. For the flue gas recirculation boiler, through the intelligent control system to adjust the amount of flue gas sent back to the combustion chamber, can better the oxygen content of the empty box air, reduce the core flame temperature.

Reduce slagging tendency of boiler

Intelligent control of boiler combustion air redistribution is achieved by closing the center hood to force more air to the sides, since the boiler combustion has a common bellows and hood in the maximum open state. Intelligent control of combustion balance can minimize the oxygen depletion zone and temperature point in the furnace and effectively reduce the slagging tendency of the boiler. By intelligent control, the feed rate of the pulverizer is improved and the fuel is transferred to the lower burner, which provides more residence time before the boiler burns out, and the flue gas temperature is kept under the ash melting temperature to minimize the possibility of slagging.

Exhaust temperature

From the overall operation of the furnace, the greatest heat loss of the furnace is taken away by the exhaust smoke. If the smoke temperature is reduced, the heat released by the smoke can be effectively reduced, so as to improve the heat efficiency of the furnace. The waste heat recovery system of the device is now equipped with an acoustic ash cleaner. In daily operation, the air preheater is used for the acoustic ash blowing of heat pipe to reduce the ash and scale accumulation of heat pipe and convection pipe and improve the efficiency of the preheater, but the effect on reducing the exhaust temperature is not obvious. During the maintenance shutdown in 2019, in addition to the transformation of the heating furnace burner, the heat pipe of the heating furnace waste heat recovery air preheater will be replaced. After the normal operation of the furnace, the exhaust temperature is 162.9℃, which exceeds the 140℃ specified in the Furnace Pipe Rules. The heat loss of the furnace is calculated as 3068KJ/kg fuel. The main reason for the analysis may be that the baffle of the flue gas direct-discharge duct of the furnace may not be closed properly, and part of the flue gas is pumped back into the air preheater again, resulting in the mismatch of smoke and air volume. According to the actual situation on site, it is planned to remove the original heat pipe preheater and replace a new air preheater at the place where the original heat pipe preheater is to reduce the exhaust temperature of the heating furnace to 110℃. In addition, the natural ventilation burner of F202 in the heating furnace waste heat recovery system is replaced with a forced ventilation burner, and the annular air duct and auxiliary air duct, fast-opening air door and baffle valve are added. The combustion-supporting air entering F202 furnace is introduced into the air preheater and then sent to F202 furnace after preheating. After the modification, the thermal efficiency of the furnace is expected to increase from 90.8% to 92.8%.

Oxygen content

The oxygen content of flue gas directly affects the thermal efficiency and safe and stable operation of heating furnace. The flue gas oxygen content is high, the thermal efficiency is low, the furnace tube is easy to oxidize; The low oxygen content of flue gas makes it easy to cause incomplete combustion. During the thermal efficiency test of the furnace, the oxygen content on-line instrument display data of the furnace are all greater than the oxygen content data of the flue gas inlet of the air preheater, the oxygen content instrument may be installed in an unreasonable position or the test is not accurate. The content of oxygen in flue gas is the main parameter that affects the combustion effect of heating furnace. The inaccurate determination of oxygen content is easy to cause insufficient fuel gas combustion, increase the loss of incomplete combustion, and decrease the thermal efficiency of heating furnace.

Operation management

Improve the operating efficiency of the automatic control system of the heating furnace, strengthen the stable control of various parameters such as the total volume, branch flow and temperature inside the heating furnace, and improve the operating efficiency of the heating furnace. There is one induced draft fan in the hydrogenation unit. Under the current practical situation, the opening degree of the flue damper of three reheating furnaces is optimized, the inlet temperature of the air preheater is controlled well, the service life of the air preheater is improved, and the exhaust temperature of the reheating furnace is reduced. In addition, operators should be regularly trained and tested to improve their operational skills and theoretical level, improve operators' understanding of the field heating furnace system, and enhance their operation guarantee technology.

Retrofit of burner

The boiler originally had 4 layers of 16 blast furnace gas burners, the first and fourth layers of burners were replaced by coke oven gas burners after the transformation. There were 8 burners in two layers, and the gas pipe, corresponding valve instrument accessories, ignition device, local control box and other accessories were replaced accordingly. The second and third layers of blast furnace gas burners were old.

Modification of heating surface

For coke oven gas calorific value is higher, coke oven gas boiler heating surface need less, the existing boiler heating surface is relatively big, will lead to the following conditions: (1) due to the chamber of a stove or furnace heating surface is too big, lead to a stove or furnace outlet flue gas temperature is reduced, superheater heat decreases, superheater steam temperature is lower than the original, can not reach the rated temperature, especially in low load condition is more serious, need to increase the superheater in the heated area. (2) Due to the large sulfur and water content in coke oven gas, too low exhaust temperature will cause serious low-temperature corrosion to the heating surface of the tail. Therefore, it is necessary to reduce the heating surface of the tail coal economizer and increase the exhaust temperature.

Reconnect the gas line

DN800 main pipe of coke oven gas shall be set up from the main network of the north ring of coke oven gas to boiler No. 5, butterfly valve, blind plate valve and corresponding metering device shall be installed, and branch pipe, four-angle pipeline and regulating valve shall be installed according to the design requirements of burner.

Modification effect

(1) After the transformation of coke oven gas, the boiler is in good running condition and all operating parameters meet the requirements, eliminating the adverse effect of high and direct mixing combustion mode of coke oven gas on boiler operation. The smoke exhaust temperature rose from the average 137℃ before the modification to the average 153℃, which greatly reduced the low-temperature corrosion of the heating surface at the end of the boiler.

(2) After the transformation, the surplus of coke oven gas in Xuangang was effectively digested, and the environmental pollution caused by the release of coke oven gas was eliminated.

(3) Reduce the amount of blast furnace gas burning, transfer to other boilers consumption, improve the steam load of other boilers, at the same time, improve the spontaneous electricity.

(4) It solves the bottleneck problem existing in the current all-fired BF gas boiler and can effectively maintain the normal operation of the turbo-blower in the case of the interruption of BF gas, thus creating conditions for the overall stability of Production in Xuangang.