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These three points must be done well in the construction of circulating fluidized bed boiler lining castables
  • Time:Mar 16, 2023
  • Views: 2

      Circulating fluidized bed boiler (referred to as CFB boiler) has become a development direction of clean combustion technology due to its advantages such as wide combustion range, cheap desulfurization, low pollutant emission, and high combustion rate.

      However, in the actual operation process, the wear and tear of CFB boilers has become a prominent problem that directly affects its economy and safety. Seriously affect the normal operation of the boiler.

      We combine the lining construction and operation of the CFB boiler to make a simple construction description.

1. Construction procedures

      The on-site construction of wear-resistant and refractory lining should be considered overall according to its lifting capacity, site size, construction period progress, climate and other conditions, and it is impossible to have a unified model. However, it is generally always possible to prefabricate the lining before the boiler components are assembled to reduce the amount of high-altitude operations after the equipment is in place. For example, boiler ignition air duct, steering flue, cyclone separator, feeder, slag discharger, etc., after the assembly and installation, the interface part is finally processed. For the convection tube bundle on the heating surface, due to the need for a hydraulic test, it is not allowed to cover the tube surface in advance. Check for kerosene leakage on the part lined with anti-wear layer on the combined surface, and the construction of the inner lining can be carried out first after it is confirmed to be qualified.

      The construction of the inner lining on the material bed cloth fan board is a more troublesome part. Since there are many hoods, the size from the surface of the inner lining must be accurate, and the inner lining material must be prevented from blocking the tuyere. Therefore, the hood should be wrapped with tape before construction. And mark the thickness of the inner lining, then carefully fill in the material layer, and pound it firmly with small tools.

2. Selection of materials

I. Castable

      (1) The price of castable is cheaper, the construction quality is easier to control, and it is suitable for large-scale construction, but its wear resistance and repair conditions are not as good as ramming material.

      (2) The vibrating construction of the castable should be done on the flat ground as far as possible, which can save the formwork, followed by the side, if it is a cylinder, it must be rolled. During on-site prefabrication, the turning and direction adjustment of components should be considered, which is restricted by the lifting capacity of construction equipment. If only partial prefabrication is possible, the bottom surface should be reserved for future operations.

      (3) The water-cement ratio of castables is crucial to the quality and must be strictly controlled.

      (4) For castables that use phosphoric acid or phosphate as a binder, the concentration and dosage of phosphoric acid should be strictly controlled. The amount of coagulant should be determined according to the temperature. It can be trial-mixed in a small batch first, and then the formal feeding operation will be done after it is suitable.

      (5) The lining with phosphoric acid or phosphate as the binder should be strictly water-free during the maintenance period. If there are no reliable waterproof measures, it cannot be constructed in the rainy season, otherwise it will lead to serious consequences.

II. Ramming material

      (1) The ramming material is easy to construct and has good performance, and is mostly used in important parts of the furnace. It is suitable for small working surface and can be constructed in the furnace, which will not affect the overall hydraulic test of the boiler. Although water is strictly prohibited during the maintenance period, it can be constructed in the rainy season.

      (2) Unlike castables, ramming materials cannot be operated on their backs, so ramming materials are used on the top of the boiler. The layer of ramming material should not be too thick at one time, and should be rammed in stages (about 2cm thick each time). After the initial setting of the material rammed last time, lay down another layer to prevent the material layer from falling due to its own weight.

      (3) The ramming material layer is easy to form a hard shell on the surface, which hinders the removal of internal moisture. When heated, the rapid expansion of water vapor will easily cause cracks and peeling off of the inner lining. Some designs require the use of 4mm diameter steel drills to pierce air holes and absorb their expansion; while some designs add flammable fibers to the inner lining to form evenly distributed micropores, which have a better effect.

      (4) The pounding material is easy to repair, and the repair area shall not be less than the range of 3 nails, and shall not be less than 300cm×300cm. If the area of the repaired old furnace is larger than 2.8m2, the furnace should be re-dried.

III. Refractory brick

      The wear-resistant brick lining is only used for cyclone separators and slag dischargers. The commonly used bricks are corundum, mullite, silicon carbide, etc. The SMG wear-resistant refractory brick developed by refractory material manufacturers is a high-quality brick with good strength and thermal stability. To be used after drying.

3. Oven

      Problem: For the construction of wear-resistant refractory materials, the requirements for the oven are determined by the set material supplier, and the oven curve table is provided. However, these manufacturers do not consider the means of ovens, which creates a technical gap and often cannot meet the oven indicators given by material manufacturers.

      Generally, circulating fluidized bed boilers are equipped with ignition devices, and oil guns are used to spray fuel to heat the ignited bed material, so they are also used as heat sources for ovens. But this kind of oven method is not ideal, the fuel oil is always sprayed to the bed surface, and the temperature of the metal wind cap of the air distribution plate on the bed surface is not allowed to exceed 1000°C. After the air distribution, the oven top and the cyclone separator The temperature does not meet the requirements. This problem may often be encountered in the installation of circulating fluidized bed boilers, and needs to be perfected in the design.

      ZHENJIN REFRACTORIES is a manufacturing enterprise integrating R&D, production, sales, international trade and technical services. The company has a production plant area of 70,000 square meters, 1 new refractory material engineering technology center, and 2 domestic first-class The horizontal microcomputer-controlled batching building and 3 ultra-high temperature tunnel kilns with intelligent automatic control system can produce 100,000 tons of refractory materials per year. With rich project experience in the lining construction of circulating fluidized bed boilers, Zhenjin Refractory always starts from the needs of customers, relies on professional scheme design capabilities and 38 years of deep cultivation in the industry, provides customers with solutions that are close to industry and business needs, and wins customers wide acclaim.

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