Gas furnace pulse combustion technology

Preface
The combustion control level of industrial furnaces directly affects various production indicators, such as product quality, energy consumption, etc. At present, domestic industrial furnaces generally adopt the form of continuous combustion control, that is, by controlling the size of fuel and combustion air flow to make the temperature and combustion atmosphere in the furnace meet the process requirements. Since this continuous combustion control method is often restricted by the regulation and measurement of fuel flow, the control effect of most industrial furnaces is not good. With the rapid development of the industrial furnace industry, pulse combustion control technology has also emerged and has been applied to a certain extent at home and abroad, and has achieved good results.
Combustion of industrial furnaces
High-end industrial products have high requirements for the uniformity of the temperature field in the furnace and the stability and controllability of the combustion atmosphere, which cannot be achieved using traditional continuous combustion control. With the emergence of wide-section and large-capacity industrial furnaces, pulse combustion control technology must be used to control the uniformity of the temperature field in the furnace.
Principles and advantages
As the name suggests, pulse combustion control adopts an intermittent combustion method, using pulse width modulation technology to achieve temperature control of the kiln by adjusting the duty cycle (on-off ratio) of the combustion time. The fuel flow rate can be pre-set through pressure adjustment. Once the burner is working, it is in full load state to ensure that the gas outlet speed during burner combustion remains unchanged. When the temperature needs to be increased, the burner combustion time is prolonged and the intermittent time is reduced; when the temperature needs to be reduced, the burner combustion time is reduced and the intermittent time is prolonged.
The main advantages of pulse combustion control are:
High heat transfer efficiency, greatly reducing energy consumption.
It can improve the uniformity of the temperature field in the furnace.
Accurate control of the combustion atmosphere can be achieved without online adjustment.
It can improve the load adjustment ratio of the burner.
The system is simple and reliable with low cost. Reduce the generation of NOx.
The adjustment ratio of ordinary burners is generally about 1:4. When the burner is working at full load, the gas flow rate, flame shape and thermal efficiency can all reach the best state. However, when the burner flow rate is close to its minimum flow rate, the thermal load is the smallest, the gas flow rate is greatly reduced, the flame shape does not meet the requirements, and the thermal efficiency drops sharply. When the high-speed burner works below 50% of the full load flow rate, the above indicators are far from the design requirements. Pulse combustion is different. No matter what the situation is, the burner has only two working states, one is full-load operation and the other is non-operation. The temperature is adjusted by adjusting the time ratio of the two states. Therefore, pulse combustion can make up for the defect of low burner adjustment ratio, and can still ensure that the burner works in the best combustion state when low-temperature control is required. When using a high-speed burner, the gas ejection speed is fast, forming a negative pressure around, sucking a large amount of kiln flue gas into the main gas, and fully mixing it, which prolongs the stagnation time of the flue gas in the kiln and increases the contact time between the flue gas and the product, thereby improving the convective heat transfer efficiency. In addition, the kiln flue gas and gas are fully mixed and stirred, so that the gas temperature is close to the kiln flue gas temperature, improving the uniformity of the kiln temperature field, and reducing the direct thermal shock of high-temperature gas on the heated body.
The adjustment of combustion atmosphere is an indispensable link to improve the performance of industrial kilns, while traditional continuous combustion control can only accurately control the combustion atmosphere in the furnace by measuring the residual oxygen content of the flue gas online, feeding it back to the combustion atmosphere controller, and then adjusting the output of the combustion air flow actuator in real time. Due to the reliability, life and price of the zirconia sensor for detecting residual oxygen in flue gas, its use in industrial sites is often not ideal. Some kiln automatic control systems simply use a proportional follower to make the flow rate of combustion air and the flow rate of fuel a fixed ratio, but this method has to leave a large surplus of combustion air, which cannot achieve the best energy saving and control of excess oxygen content (or excess air coefficient). The pulse combustion control method can adjust the oil pressure and wind pressure to the appropriate value at one time. After the system is put into operation, it is only necessary to keep these two pressures stable. It is much simpler to measure and control the pressure than the flow rate. It can be fully automatically controlled according to the actual situation of the system, or it can be manually controlled. Compared with continuous combustion control, the pulse combustion control system has greatly reduced the number of instruments involved in the control, only temperature sensors, controllers and actuators, and a large number of expensive flow and pressure detection control mechanisms are omitted. In addition, since only two-position switch control is required, the actuator is also changed from the original pneumatic (electric) valve to an electromagnetic valve, which increases the reliability of the system and greatly reduces the system cost.