The correct blow in method and process is the key to CFB boiler service life. This blow in project refers to electric roasting and traditional coke roasting plus electric roasting method, mainly adopts electric roasting, combined with a little amount of wood roasting or coke roasting. The main purpose is to improve roasting effect and to prolong furnace lining life.
CFB boiler blow-in is divided into 3 stages:
1. wood or coke roasting electrode, moisture removal and furnace preheating;
2. electric roasting electrode, furnace heat regeneration;
3. Burdening material to establish reaction system. The purpose of blow in craft is to remove moisture, ensure the good sintering of 2.5~3m long electrode working end, regenerate heat and provide suitable condition for reaction. The main steps for CFB boiler blow in are as follows:
- Blow-in preparation
- check and adjust all the main equipment and auxiliary equipment, which mainly include: water recycling equipment, insulation equipment, electrode clamping and lifting equipment, high voltage and low voltage electrical equipment, etc, ensuring the good operation condition of all systems.
- Furnace roasting material supply: wood 50t, coke (with 40~100mm granularity) 20t, small quantity of kindling waste oil.
- Wood or coke roasting electrode and furnace body
CFB boiler furnace bottom and furnace wall should be loaded with a little amount of wood and ignited by waste oil, so furnace body and electrode can be roasted. At this step, the main purpose is removing moisture and roasting electrode. Furnace hearth should maintain small fire, to make sure the even distribution of heat, coke should be continuously charged into the lifting cage to promise electrode sintering.
Wood roasting or coke roasting should last for 72h, at late wood roasting period, please check electrode roasting condition, so the roasting time can be adjusted accordingly.
- Electric roasting
Electric roasting is the core stage for CFB boiler blow in. Electric roasting method is: 3-phase electrodes should ground connected from furnace bottom, so there is no arc generated, electric energy can directly conducted into furnace bottom and generate heat energy. Items should be paid attention to are as follows:
- Clean furnace hearth lifting cage and carbon ash.
- Similar to wood roasting preparation step, inspect and adjust all the operation systems again.
- Adjust transformer high voltage connection method, promise the proper voltage.
- F8~10mm thickness steel boards should be paved at furnace bottom, right under the electrodes, so conduction columns can be installed on them. The height of conduction column is about 1200mm, inner steel board diameter is about 800mm larger than electrode diameter, outer steel board diameter is about 600mm larger than inner diameter.
- Adjust electrode working end length to about 2500~3000mm, and electrode end face should tightly pressed on conduction column coke grains(0~10mm diameter).
- Rest part of furnace bottom is paved with 300mm thick, 10~20mm granularity coke.
- Check relevant equipment again, power on for roasting. During switching on power, quickly switch on and switch off for 3 times, to check whether 3-phase voltage is balanced or not, whether short net is short circuit or not.
- Furnace blow-in with 70V lowest power, roasting for about 8 days, the total powder consumption is about 800,000 KWh.
- Electric roasting should comply with the rule of gradually increase the load, intermittent switch off the power to make furnace temperature homogeneous, electric roasting should be carried out strictly according to roasting regulations.
- During electric roasting, coke should timely added into conduction column, equipment operation condition should be observed and recycling water should be adjusted.
- If the furnace is shut down by some reasons, when switching on the power, voltage should be gradually increased from lowest grade to higher grade.
- Prepare furnace burden during roasting period, before charging furnace burden, furnace bottom should charge 20t coke granule, the thickness is about 300~500mm.
