In the process of reforming coal-fired boiler into gas-fired boiler, it should be based on the principle of not changing the pressure parts of boiler body and reducing the original boiler. The innovation process should focus on the selection of gas incinerators, the determination of the number of incinerators, the installation of incinerators, the compatibility plan of furnace installation, the selection of explosion-proof mistakes and other aspects, and follow the rules, not only considering the economic benefits, but also from the applicability.
Selection of gas incinerator
In the course of coal-fired boiler innovation, it is necessary to select or plan appropriate gas incinerators. The common gas incinerators can be divided into three types according to the method of providing atmosphere, i.e. ejective incinerator, blast incinerator and spontaneous combustion induced air incinerator. The atmosphere required by the induced combustion is inhaled by the gas jet. The air blast incinerator needs to blow the building to send the atmosphere into the combustion system, while the natural induced air incinerator relies on the negative pressure in the furnace to suck the atmosphere required by the combustion into the combustion system.
1. The selection and response of the incinerator should be considered in comparison with the characteristics of the three kinds of incinerators and the characteristics of the original furnace of the steam boiler.
1) the safety level of the gas incinerator, that is to say, it is required that the low-level gas is not completely incinerated for thermal damage. The thoroughness of incineration is related to the uniformity of gas and atmosphere and the adequacy of atmosphere. Generally, it is not difficult to lose the negative gas completely without burning under the condition of sufficient atmosphere and superior mixture. When burning high calorific value gas, the damage caused by incomplete burning of gas shall not exceed 0.5%; when burning low calorific value gas, the damage caused by incomplete burning of gas shall not exceed 1.5%. When accepting the premixed incinerator, it is easy to control the incomplete incineration damage a little lower than that of the scattered incineration.
2) the redundant atmosphere coefficient in low smoke is a useful error in low smoke destruction. The sum of the amount of excess atmosphere in the exhaust gas and the amount of atmosphere leaked into the flue gas channel. For the boiler operated under micro positive pressure, the atmosphere leaked into the flue gas channel is zero. At this time, it is important that the amount of excess atmosphere depends on the amount of excess atmosphere during incineration. In reality, under the working environment, the amount of excess atmosphere during incineration will play an important role in improving the thermal compliance of the boiler. Whether the incinerator can be guaranteed to operate in spite of low excess atmosphere coefficient is one of the tight targets of the incinerator.
3) the flame characteristics of the incinerator are intimately related to the heat exchange in the furnace and other characteristics of the boiler. For example, in the case of decentralized incineration, the semi luminous flame is stronger than the flame radiation in the case of flameless incineration, which is beneficial for spreading in the furnace. The air flow at the burner nozzle should have a higher speed and a larger range, so as to make the flame filling degree in the furnace better. When using refractory to enhance heat transfer in the furnace, the flame pattern and flame rate corresponding to the radiation surface are required.
4) sufficient consideration of incineration rate. Because high-speed incineration is the trend of the development of small and medium-sized steam boiler, it can reduce the size of incinerator and furnace, which is the nervous miss of the miniaturization of steam boiler and the nervous characteristic target of incinerator. However, in the actual manufacturing, because small and medium-sized steam boilers are often used in the environment of variable load, so the request incinerator has a wide range of load adjustment limitations. During the operation of the innovated gas-fired boiler, the filling degree of the furnace flame shall be well controlled, so as not to cause the dead angle of the air flow, and avoid the flame of the adjacent incinerators disturbing each other. Meanwhile, the unburned gas and the air inclusions shall not touch the heat exchange surface, so as to avoid the incomplete burning of the gas. However, to avoid high-speed flushing of the heat exchange surface, the high heat intensity of the heat exchange surface can not make the pipe wall overheat. Therefore, when choosing the incinerator, it is necessary to use different fuel gas and load, similar to the estimated length of the burning flame.
2. Number of gas incinerators is confirmed
The number of gas burners in the innovation of coal-fired boiler can be determined by the following formula:
n=Qgl/Qrq
Where, n is the number of gas incinerators; qgl is the heat load capacity of steam boiler, kW; qrq is the heat load of single incinerator, kW. In the practical innovation, in order to prevent the explosion or explosion of a certain incinerator caused by disorderly flameout when multiple incinerators are running at the same time, the number of gas incinerators generally does not exceed 4. In order to deal with the problem of flameout and tempering when the gas flow of the boiler is lower than that found at low load, it can be experienced to install an oil gun in the incinerator to comply with the change of the boiler at low load, and the flameout and explosion-proof assembly shall be jointly arranged in the furnace.
3. Installation of incinerator
1) the flame shall be placed in the middle of the furnace to fill the furnace as much as possible, and the combustion shall be consolidated.
2) the flame is located in many middle areas of the furnace, which can evenly distribute the heat in the furnace, and will not cause stress increase caused by partial heating, so as to prevent uneven heating, and avoid overheating of the heated part in the boiler.
3) the furnace depth of horizontal steam boiler is large, and the incinerator is installed on the front wall of the furnace to ensure that the front smoke box will not overheat. At present, the domestic small and medium-sized coal-fired boiler can be divided into two types according to the incineration method: layer incineration and chamber incineration. There are countless layer burning furnaces, which are chain furnaces, characterized by the combustion of fuel in the furnace with constant or sluggish action. When the innovated boiler is a chain boiler, the external style of its front and rear walls and furnace arch is inconvenient for the placement of the incinerator, so the gas incinerator should be placed on the south side of the chain boiler. In order to make the heat exchange state in the furnace after innovation similar to that before innovation, so as to reduce the change of the heat exchange building in the chain furnace, the gas incinerator shall be placed under the middle of the furnace side wall. As for the pulverized coal boiler, in order to connect the characteristics of the furnace atmosphere energy field similar to that before the innovation and reduce the innovation work quantity, it is feasible to install a new incinerator based on the position of the original pulverized coal incinerator nozzle
——Author：ebico