Pulse combustion technology of gas stove

As the name implies, pulse combustion control is an intermittent combustion mode, and the temperature control of the kiln is realized by adjusting the duty ratio (on-off ratio) of combustion time by using pulse width modulation technology. The fuel flow can be preset by pressure adjustment, and once the burner works, it will be in a full load state, ensuring that the gas outlet speed of the burner will not change. When the temperature needs to be raised, the combustion time of the burner is prolonged and the intermittent time is reduced; When cooling is needed, the combustion time of the burner is reduced and the intermittent time is prolonged. See figure 1 for the control chart.

The main advantages of pulse combustion control are:

High heat transfer efficiency, greatly reducing energy consumption.

The uniformity of the temperature field in the furnace can be improved.

Accurate control of combustion atmosphere can be achieved without on-line adjustment.

The load regulation ratio of the burner can be improved.

The system is simple, reliable and low cost. Reduce the production of nitrogen oxides.

The regulation ratio of common burners is generally around 1: 4. When the burner works at full load, the gas flow, flame shape and thermal efficiency can reach the best state. When the burner flow is close to its minimum flow, the heat load is minimum, the gas flow is greatly reduced, the flame shape can not meet the requirements, and the thermal efficiency drops sharply. When the high-speed burner works below 50% full load flow, the above indexes are far from the design requirements. This is not the case with pulse combustion. In any case, the burner has only two working states, one is working at full load, the other is not working, and the temperature can be adjusted only by adjusting the time ratio of the two states. Therefore, pulse combustion can make up for the defect of low regulation ratio of the burner, and the burner can still work in the best combustion state when low temperature control is needed. When the high-speed burner is used, the gas injection speed is fast, so that negative pressure is formed around it, so that a large amount of flue gas in the kiln is sucked into the main gas and fully stirred and mixed, which prolongs the residence time of flue gas in the kiln and increases the contact time between flue gas and products, thus improving the convective thermal efficiency. In addition, the flue gas and gas in the kiln are fully stirred and mixed, so that the temperature of the gas is close to the temperature in the kiln, the uniformity of the temperature field in the kiln is improved, and the direct thermal impact of the high-temperature gas on the heated object is reduced.

The adjustment of combustion atmosphere is an essential link to improve the performance of industrial furnaces, while the traditional continuous combustion control can only accurately control the combustion atmosphere in the furnace by measuring the residual oxygen in the flue gas online and feeding it back to the combustion atmosphere controller, and then adjusting and controlling the output of the combustion-supporting air flow actuator in real time. Because of the reliability, life and price of zirconia sensor for detecting residual oxygen in flue gas, it is often not ideal in industrial field. Some kiln automatic control systems simply use proportional followers to make the flow of combustion-supporting air in a fixed proportion with the flow of fuel, but this method leaves a large amount of surplus combustion-supporting air, which cannot meet the requirements of optimal energy saving and control of excess oxygen content (or excess air coefficient). Using pulse combustion control mode, oil pressure and wind pressure can be adjusted to appropriate values at one time. After the system is put into operation, it is only necessary to keep these two pressures stable. The measurement and control of pressure is much simpler than flow, and it can be controlled automatically or manually according to the actual situation of the system.

Compared with continuous combustion control, the pulse combustion control system involves fewer instruments, only temperature sensors, controllers and actuators, which saves a lot of expensive flow and pressure detection and control mechanisms. Moreover, because only two-position switch control is needed, the original pneumatic (electric) valve is changed into electromagnetic valve, which increases the reliability of the system and greatly reduces the cost of the system. The industrial furnace control system adopts industrial PC as the control unit and adopts advanced field bus architecture, which has powerful functions, rich pictures and friendly user interface. All components are imported products, which makes the system more reliable.

The system has the following functions:

Real-time monitoring of temperature, residual oxygen in flue gas, furnace pressure, oil (gas) pressure, combustion-supporting wind pressure, fuel flow and combustion-supporting air volume at all points in the furnace.

With up and down alarm function and alarm printing function. The upper and lower alarm limits are set by users, and alarm records can be stored, and users can query and print them at will.

According to the temperature value or temperature curve set by the user (see the figure below), the temperature of each section in the furnace can be controlled by pulse combustion and the temperature can be controlled by forced pulse air cooling.

The residual oxygen in the flue gas can be controlled according to the combustion atmosphere set by the user.

The furnace pressure can be controlled.

The feeding and discharging of the kiln can be controlled.

It has the function of historical data query, and can store, display and print historical data according to users' needs.

It has report printing function, and can print class newspaper, daily newspaper and monthly report offline in real time.

It has a dynamic process diagram, which can display the process flow diagram of the whole furnace, the parameters of each point in the furnace and the flame combustion state in the furnace in real time.

In practical application, when the common pulse width modulation is used to adjust the combustion duty ratio, when the duty ratio is close to 0% or 100%, the intermittent or combustion time is too short, and the field operation effect is not ideal, so we introduce the concept of minimum time, set the minimum time of intermittent and combustion to 3 seconds, and extend the corresponding combustion and intermittent time when the duty ratio is close to 0% or 100%. As a new technology, pulse combustion has broad application prospects and can be widely used in ceramics, metallurgy, petrochemical and other industries. It will play an important role in improving product quality, reducing fuel consumption and reducing pollution. It is an innovation of automatic control in industrial furnace industry and will become the development direction of industrial furnace combustion technology in the future.

1. This equipment takes various combustion gases as medium and is heated by various burners. The highest temperature is 1200℃.

2. The furnace body frame is made of various large and medium-sized section steel welded on site, the shell sealing plate is colored steel plate, and the high-aluminum all-fiber fire-resistant silk-throwing carpet module is furnace lining, so the sealing and energy-saving effect is obvious.

3. The trolley frame is welded by various large I-beams, channel steels, angle steels and thick steel plates.

4. The car is driven by all wheels and has reliable performance. The transmission system adopts "three-in-one" motor-reducer shaft installation mode, with compact structure, firm assembly, flexible access, simple operation and convenient maintenance.

5. The refractory masonry of trolley adopts high-alumina special-shaped brick structure, which has good sealing effect with furnace body and high compressive strength. The shim is placed on the surface of the trolley for stacking workpieces. The side plates of the trolley are all cast to ensure that the car body is not deformed and durable. The sealing between the trolley and the furnace lining adopts the automatic pressing structure of electric push rod with refractory fiber sealing block. The opening and closing of the side seal are interlocked with the entry and exit of the furnace car.

6. The oven door is made of high-alumina all-fiber fire-resistant wire-throwing carpet and steel composite frame structure, and the electric hoist is lifted. The oven door sealing mechanism adopts long and short lever spring type automatic compression cam mechanism and soft edge sealing device. Ensure no friction up and down, easy, safe and reliable.

7. The chimney is equipped with automatic furnace pressure control and butterfly valve, which can adjust the cooling rate.

8, heating adopts high-speed burner, evenly distributed on both sides. Continuous proportional adjustment combustion. The actuator adjusts the air quantity, and the gas quantity is adjusted by the proportional valve to realize air-fuel ratio combustion. The amount of gas and air is limited by the lower limit. The gas pipe of each burner is equipped with a control solenoid valve, and each burner is equipped with an independent and complete combustion controller, which has the functions of automatic ignition, flame detection, fire alarm and automatic gas cut-off. This fully ensures the stability and safety of the combustion temperature control system.

9. Characteristics of burner

High-speed burner means that fuel and combustion-supporting air are basically completely burned in the combustion chamber, and the high-temperature gas after combustion is ejected at the speed of 100m- 150m/s, so as to strengthen convective heat transfer, promote air circulation in the furnace, achieve the purpose of uniform furnace temperature, and make the heat preservation uniform at ≤ 10℃.

combustor

First, the combustion chamber is small.

B, the combustion gas outlet speed is high

C, burner adjustment ratio is large, 1: 10.

D, automatic ignition and flame monitoring

E, each burner fault alarm function

F, the combustion air under-voltage protection.

G. Safety control of large and small fire chains of each burner.

H, combustion status display, fault alarm display

I design, modify, save and print temperature curves.

J, operation tips, fault tips

K, combustion fan control (switch), oven door control (switch), air-fuel ratio control, process safety interlock control

10, preheater

The GC tube heat exchanger with spoiler is used to increase the air preheating temperature, and the air temperature is preheated to 300-350℃ when the furnace temperature is 1000℃.

Under the same heat transfer coefficient, the pressure loss on the empty side of GC high-efficiency plug-in heat exchanger is lower than that of ordinary plug-in heat exchanger, which is about 1500Pa, thus reducing power consumption.

When the flue gas temperature is 600℃, the comprehensive heat transfer coefficient is above 45W/M2℃, and when the flue gas temperature is above 900℃, the comprehensive heat transfer coefficient is above 55 W/M2℃.

The heat exchanger is designed with heat-resistant steel and stainless steel according to different temperatures, and the arrangement adopts temperature homogenization and thermal stress elimination measures.

1 1, control system

The system mainly adjusts and controls the gas pipeline flow, flue gas flow and dilution air flow of each furnace by detecting the temperature and pressure of the furnace, and is equipped with a quick cut-off device for natural gas main pipe.

Furnace pressure has a great influence on the use effect of heating furnace. When the furnace pressure is high, the furnace gas will rush out from the sealing gap of the furnace body, forming airflow erosion, which has a great impact on the furnace door and furnace bottom sealed with fiber materials. At the same time, the high temperature airflow will also affect the surrounding environment and control devices of the furnace body. When pressing the furnace, cold air is sucked out from the sealing gap, which not only increases the oxidation of the workpiece, but also makes the high temperature in the furnace be quickly drawn out by negative pressure, resulting in fuel waste. Therefore, the furnace pressure measuring point on the exhaust flue controls the electric regulating flue gas valve to keep the furnace pressure in a slightly positive pressure state.

The furnace is controlled by zone temperature, and each zone is equipped with thermocouple. The measured temperature enters the multi-point recorder to track and record the temperature in the furnace centrally.

12, safety interlock system

When the oven door is not opened to a certain position, the trolley will lock in and out, and when the trolley seal is not opened, the trolley will lock in and out.

When the pressure of air, gas and compressed air fails to meet the specified requirements, the burner will not start, and if it is burning, it will be safely shut down.

13, the main features of the equipment

1, good energy-saving effect: the furnace lining of the furnace body of this equipment is all made of high-alumina refractory fiber, which has small thermal conductivity and heat capacity compared with refractory bricks, so the thickness of refractory layer is small and the heat absorption is greatly reduced.

The equipment adopts high-speed temperature regulating burner system, and the injection speed is as high as 100m/s, which can effectively stir the furnace gas, make the furnace temperature uniform, make the burner system burn completely, and make full use of fuel. By adopting zero furnace pressure control and full sealing technology, the maximum joint surface (the sealing surface between the furnace car and the furnace body) is at zero furnace pressure, so that the furnace gas does not leak out and the cold air does not penetrate, and the heat energy generated by combustion can be effectively utilized.

2. High degree of automation: both the oven door and the oven car are electric, and there is an operation console, so operators can easily control the operation of the oven door and the oven car. The oven door and locomotive are controlled by their travel, and can automatically stop running when reaching the limit position to ensure safety.

The combustion system has a complete set of functions of ignition, large and small fire operation, detection, flameout alarm, flameout cut-off and reburning, and each set of burners has an independent control box, which can be controlled independently. The interface of each control box can be connected with the temperature controller between instruments, thus realizing the automatic control of the whole system.

Pipeline parameters are automatically controlled. The pipeline pressure of combustion-supporting air and fuel can be set and automatically adjusted, so that the amount of combustion-supporting air and fuel can be controlled in the best ratio, the combustion efficiency is ensured, and black smoke is eliminated.

Automatic control of furnace pressure, which compares the furnace pressure signal with the set value through the pressure transmitter and transmits the signal to the actuator of the chimney, and automatically controls the pressure in the furnace by changing the opening of the chimney.

The temperature control in the furnace adopts advanced intelligent digital display temperature controller, which forms closed-loop control with temperature measuring elements and automatic burners. It has high precision, high flexibility, anti-interference and high reliability. The temperature control system can automatically calculate, calculate, display and store the process curve of heat treatment production, and realize the whole process control.

The instrument cabinet is equipped with operating value display of temperature, furnace pressure, burner and pipeline parameters, abnormal alarm and emergency protection measures to ensure safe operation.

Hot standby sequence and transfer to production sequence

1. Any water jacket leakage or stirring rod leakage should not be converted into a hot standby furnace. Where the air branch valve is not tightly closed or the saturated steam valve leaks seriously and cannot be overhauled and replaced during hot standby, it is not suitable for hot standby.

2. When planning hot standby, manufacturers with good furnace conditions should be selected for hot standby. If the fire layer drops, serious slagging will occur in the furnace, which will inevitably worsen the furnace condition.

3. For the planned hot standby generator, the furnace should be explored in advance, and a small amount of slagging parts should be brazed, and brazing should be carried out at various points in the furnace section to make the furnace section basically elastic.

4. Reduce the ash layer appropriately.

5. Thicken the coal seam appropriately.

6. Check whether the bell cover of the maximum safety valve rises and falls flexibly.

7. Reduce the air volume before hot standby.

8. Seal the double riser water seal, and pull up the maximum safety valve in time according to the outlet pressure of the furnace.

9. Close the branch air valve and saturated steam valve.