Application case 24: Heavy-oil combustion technology of glass furnace and energy saving

Heavy oil is an important fuel with high calorific value, glass melting furnace has used heavy oil to melting glass for 40 years of history in china, in recent years the new and expanded kiln of dozens of large and medium-sized float glass production line mostly are using heavy oil heating. For decades, especially in recent years, through our actively developing and constantly absorbing, digesting the foreign advanced experience, the heavy oil combustion technology of glass furnace has make a spurt of progress of development in China, and vigorously promoting the advanced combustion technology, will play a strong role in promoting the further improvement of yield and quality of our glass products, reducing energy consumption and production costs.

1．Selection and energy saving of fuel spray gun

The fuel spray gun is a burner which can make the heavy oil atomization, and format the flame with a certain shape, length and direction. Different types and structure of spray gun will have different atomization effect on the heavy oil, it has a great relationship with whether full combustion or save energy. Therefore, in the heavy oil combustion system, you must select the fuel spray gun, of which the effect on atomization and combustion is good.

For a long time, our country mainly used the Soviet Union went the gun, which is the high pressure mixed DC type spray gun using steam or compressed air to atomize, utilizing the high speed airflow of atomizing medium to meet the heavy oil flow at the gun exit to produce adiabatic expansion and then atomizing. The atomization performance of it is poor; the flame has 20~30cm long coarse atomization area. Combustion is not full, fuel consumption is high; gas consumption of atomization is high, causing a great waste of energy. Later, our country used the imported German sorg lance and the United States OI spray coffin. However, because of its atomization principle is simple, or limitations of the structure exist, the effect is not ideal. Then, our country has introduced the British Rand Luo gun, this is a good gun which is well known in the world, but the gun is suitable for heavy oil with low viscosity, low moisture content, low impurities, obviously cannot meet high viscosity, high moisture, high impurity of heavy oil or residual oil which is widely used on China's glass factory, thus, the use effect is not ideal, the fuel saving rate is only 3% ~ 5%. In this case, Engineering and technical personnel in China, through the unremittingly efforts, has successfully developed China CMT-900 fuel spray gun. This gun is not only in the technical performance comparable to the RAND Luo spray gun, and the most suitable for high viscosity fuel in China, can completely replace the various types of fuel spray gun from abroad.

The CMT-900 gun is a oil film type double critical pressure spray gun using compressed air or steam as the atomizing medium, the principle of the atomization is that: firstly heavy oil flow is formed a layer of oil film on the inner surface of the swirl spray gun; and the atomizing gas which is through the surface of swirl vitro, is depressed to the critical pressure in a rotary fluid outlet, and then form the critical speed and huge gas power, to break up the meeting oil film for the first time atomization. When the mixture of oil and gas arrives at the gun exit, airflow pressure is depressed to the critical pressure again, and carries on second times of atomization of oil mist. that atomization process is perfect, particle size of heavy oil is fine and uniform, the oil mist diameter even is 30~50 micron, thus evaporate quickly, complete combustion, the flame brightness, heat radiation, high heat transfer efficiency, fuel saving rate can reach 7% ~ 12%,it is 4% ~ 7% higher than the use of Rand Luo gun.

CMT-900 fuel gun is an energy-efficient excellent spray gun, currently most flat glass factory use it in china.

2．The control of fuel oil viscosity

One of the characteristics of heavy oil is high freezing point, high viscosity. Bull is a main contradiction of heavy oil combustion system, when the heating temperature is not enough, the viscosity is large, the atomization conditions of the gun will worsen; overheating will cause heavy oil cracking and foaming, resulting in unstable combustion. Therefore, the reasonable heating oil, makes the viscosity accord with the requirement of the use of spray gun, is important to guarantee the good combustion and energy saving.

For the control of the fuel oil viscosity, people used to adopt directly control the heating temperature and indirect control of the fuel oil viscosity, which is realized by the relationship of corresponding values between temperature and viscosity of heavy oil, however, because of the different oil types, the corresponding values of temperature and viscosity of oil are different, so this needs to be determined through the experimental method. The method of temperature control viscosity, although simple, the use is very common, but there exists such problems: when oil type is changed, we are often too late to determine change the corresponding value of temperature and viscosity of oil, unable to adjust the heating temperature timely, the phenomenon of out of control of fuel oil viscosity will appear, influencing the normal fuel combustion, therefore, this is not the ideal viscosity control method.

The latest fuel oil viscosity control method is the cascade control method of oil viscosity and oil temperature, namely using the fuel oil viscosity control heating temperature, and then using heating temperature control the fuel oil viscosity. The oil-way in the oil heating device is provided with a viscometer, using the viscosity value of the fuel oil required by spray gun as the value of viscometer. Using the given value of viscometer as the directive of fuel heating temperature of automatic control, finally using the heating temperature required by this directive to stabilize the fuel oil viscosity. Therefore, No matter how the viscosity characteristics of oil change, oil heating device always automatically adjust the heating temperature of the fuel oil in accordance with the given value of viscosity, to make the fuel oil viscosity after heating to meet the requirements of gun use. This method of control, high degree of automation, viscosity control timely, accurate and stable, obvious energy saving effect, we can say that, this is a kind of ideal viscosity control method, Should be widely used.

3 The control of furnace temperature

Fuel flow directly affects the temperature of melting furnace, we usually by adjusting the fuel flow to control the furnace temperature and the melting condition. It is that setting a plurality of temperature signal along the length direction of furnace to represent the temperature of melting furnace for glass melting process. When the temperature signal changes, fuel flow control system will automatically increase or decrease the fuel flow, to make the temperature of melting furnace bake to control indicators. However, the temperature signal is greatly influenced by various factors, changes frequently, therefore, very prone to misleading and blindness of oil quantity regulating. In this way, not only a great waste of fuel is caused, but also the stability of the temperature of melting furnace is hard maintained. Obviously, the method of adjusting the fuel flow to control the temperature of melting furnace is not desirable.

In fact, in many factors that affect the furnace temperature, the maximum and most frequent disturbance is the change in fuel flow. Stable fuel flow, eliminate interference of fuel flow change, and then the temperature of melting furnace can remain stable. Using the method of adopting fixed value to control the furnace fuel flow, in order to stabilize the oil supply of each small furnace, and then indirectly achieve the purpose of making the temperature control of melting furnace stable. This is that, firstly, according to the amount of melting furnace and melting temperature curve, and in combination with production experience, to calculate the amount of fuel oil required by each furnace, which is used as the given value of small furnace oil, and then input control system, and through the given value to implement the set value control of the fuel flow of all small furnace in the practical production, ensuring supply stable.

Generally, the given value of small furnace oil quantity is not changed; this can make the temperature of melting furnace to maintain the stability for a long time. That constant value control small furnace oil, can realize the stable control of the temperature of the melting furnace, and achieve energy saving effect. So, everyone recognized that, this is the best way to control the temperature of melting furnace.

4 The intelligent control technology of dynamic optimization algorithm to achieve the optimizing combustion of fuel oil

The optimizing combustion is that, in the good quality of atomization and the reasonable combustion conditions, the fuel oil achieves sufficient combustion.

The atomization quality of fuel, not only has a close relationship with the structure of spray gun and the viscosity of the fuel oil, but also is closely related with the atomization gas flow. If the quantity of atomization air is not enough, the atomization quality will not be good, affects the full combustion; if the quantity of atomization air is surplus, the atomization effect will not be improved, results in waste of atomization. The so-called rational combustion condition is that, the fuel oil is full combusting in the lowest excess coefficient of air. If the excess air coefficient is too small, the quantity of combustion air is prone to not enough, resulting in incomplete combustion, wasting fuel; If the excess air coefficient is to large, the combustion process will be weaken, and take away a lot of heat through the smoke, thermal efficiency will be affected. To ensure good atomization and reasonable combustion conditions, must be in accordance with the reasonable the gas-oil ratio and the air-fuel ratio, to quantitative control of the quantity of atomization air and combustion air, under the combustion condition, to ensure the fuel in any situations of air flow can obtain the reasonable quantity of atomization gas and combustion air, and realize good atomization and the full combustion.

The gas-oil ratio is the reasonable gas oil ratio which is determined by experimental method during the design process of spray gun, because the flame is made to be brighter, so the temperature difference is small along the flame length. In the production process, according to the flame status in furnace, timely artificial modify the using atomization gas and combustion air, to ensure that the using gas-oil ratio is always rational.

The air fuel ratio is determined according to the oxygen content in the smoke, while the oxygen content is reduced by 1%, 2% of fuel oil can be saved. The reasonable air fuel ratio should make the oxygen content in the smoke keep in the range of 2% ~ 5% after the fuel oil combusts. A portable oxygen measuring instrument can be used to indirectly measure the oxygen content in the flue gas, and then based on the measured value to artificial modify the using air-fuel ratio; or through the online automatic measuring device of oxygen to automatically continuous detect the oxygen content in the smoke, and according to the measured value to automatic correct the air fuel ratio, to ensure that the used air fuel ratio is always the reasonable air fuel ratio. Realizing the optimizing combustion can save 1% ~ 3% of fuel.

5 The control of flame reversing

In the process of flame reversing, melting furnace has a few seconds ~20 seconds to stop flameout, stop atomization gas, and stop combustion air, during this time the normal thermal system of furnace is damaged, various parameters of furnace have great disturbance, oxygen content of kiln temperature, kiln pressure and smoke will have great changes. After changing the fire, in order to keep the kiln temperature, kiln pressure unchanged, when one side of flameout recovers to combust, it will be greatly increased the amount of fuel, combustion air, and atomization gas. But in fact, the heat capacity of glass liquid is great, it will not cause the great cooling because of the short time ceasefire, which needs greatly increase the amount of fuel, and causes unnecessary waste of fuel. In addition, if increasing the amount of fuel, but the amount of atomization gas and the combustion air volume do not follow to go up, the incomplete combustion also will be caused, making the black smoke out from the chimney. In order to avoid the waste of energy, when changing the fire, adopting the method of locking parameters such as fuel quantity, the amount of atomization gas, combustion air volume, the kiln temperature, kiln pressure, the oxygen content of the flue gas before changing the fire, to stabilize the furnace condition. At this time, regardless of whether the kiln temperature, kiln pressure changes, the amount of fuel and other parameters do not change. After changing the fire for a certain time, the fuel quantity parameters etc will be unlocked, to restore the normal operation, the unlocking time were: the amount of fuel, atomization gas and combustion air volume: 5 seconds; kiln pressure: 20 seconds; kiln temperature: 60 seconds; flue gas oxygen content: 3.

When reversal, the control method of locking related parameters can effectively overcome the large disturbance of the reversal process to the melting, and achieve that target, using the least fuel consumption in the shortest time to make the thermal system of the melting furnace stable, which can save 1% of fuel oil.