Discussion on Refractory Materials of Circulating Fluidized Bed Boiler

September 14, 2021

1. Current status of refractory materials for circulating fluidized bed boilers

 

At present, the types of wear-resistant refractory materials commonly used in circulating fluidized bed boilers (CFBB) in China are: phosphate bricks and castables, sillimanite bricks and castables; silicon carbide bricks and castables; corundum bricks and castables; Wear-resistant refractory bricks and castables; the most high-end products include silicon nitride and silicon carbide products.

 

Judging from the results of the existing CFBB use, the use effect of these materials is not very satisfactory. According to the use of these refractory materials, we make the following analysis of the performance and cost of refractory materials: Phosphate bricks are non-burned bricks heat-treated at low temperature (500℃), usually used in the range of 1200~1600, and are used in cement kilns. For many years, because CFBB operates in the range of 850°C to 900°C, the physical properties of the refractory material are unstable at this temperature, and the wear resistance performance cannot be fully exerted. The physical and chemical properties of phosphate-fired injection are the same as bricks. The difference is that its construction is more complicated and restricted by the environment. The construction personnel are required to have certain professional skills. Such as improper construction, the quality cannot be guaranteed, which has been understood by many manufacturers. Although the use of phosphate materials on CFBB has its shortcomings, its price can be accepted by various manufacturers.

 

Zhengzhou Rongsheng

 

Sillimanite is a high-quality refractory raw material. It is usually added to refractory materials to increase the load softening temperature by 100~150℃. Sillimanite brick is an ideal wear-resistant refractory material when used on CFB. However, the sillimanite castable cannot reach its sintering temperature range due to the combustion of CFBB, and the wear resistance of sillimanite cannot be fully utilized. In addition, the price of sillimanite material itself is relatively high, and the price of the produced product is also high, which increases users. The cost, these affect the promotion and application of sillimanite castables on CFBB.

 

Silicon carbide products have good wear resistance and good thermal shock stability when used in a high-temperature, non-oxidizing atmosphere. The surface can form a glaze protective layer when sintered at a certain temperature. According to the situation of individual domestic users, It can't get satisfactory results when used on CFBB. The main reason is that there is an oxidizing atmosphere in CFBB combustion, and at the same time, its price is relatively high. Good materials have not been reasonably used, and users cannot produce good economic benefits, which is also a waste.
 
Zhengzhou Rongsheng

 

The above-mentioned refractory materials for CFBB are representative in China. According to the understanding of most users, users have different feedbacks and there are many problems. The main reason is that various boiler manufacturers and design units choose refractory materials in many varieties, and there is no uniform standard. There are few refractory materials that have high wear resistance, can achieve the same cycle operation as the furnace, the same periodic maintenance, and can produce good economic value and social benefits.

 

The refractory materials used in the early domestic 35 t/h and 75 t/h CFBB were basically based on the refractory materials used in related industries (such as metallurgy and petrochemical). The requirements for slag resistance are different. CFBB requires refractory materials to have high temperature wear resistance and high thermal shock stability. During construction, it requires layered construction and cementation of wear-resistant refractory materials and heat preservation sealing materials, that is, heavy and light, shaped and unshaped. For supporting construction, refractory materials with different production processes and different construction methods require the same indicators.

 

Zhengzhou Rongsheng

 

With the introduction of foreign CFBB technology, some domestic CFBB design manufacturers have formulated technical requirements for refractory materials based on the requirements of foreign companies for CFBB refractories, supplementing and perfecting the domestic CFBB refractory material standard system, but currently domestic boilers Manufacturers and design units have their own opinions. There is a certain degree of blindness in the selection of materials by users. In addition, the quality of products of some manufacturers is not good. After the construction and installation of refractory materials, large areas of collapse or wear occurred within 72 hours of operation. The result is Users not only spent a lot of money, but couldn't meet their needs, which caused great economic losses to production and adversely affected the promotion and application of CFBB.

 

2. Recommendations for the selection, installation and maintenance of refractory materials

 

In the absence of a uniform standard for refractory materials for CFBB in China, we suggest that when designing units and manufacturers choose refractory materials, they should hire professional and technical personnel and experts with practical experience to evaluate and demonstrate the following content in order to achieve Specific needs such as wear resistance and high temperature resistance.

 

1) Whether the selected refractory material is specially developed for CFBB use;

 

2) Whether the physical and chemical properties of refractory materials can meet the special performance requirements of CFBB;

 

3) Whether the physical and chemical properties of refractory materials have been inspected by the national authority, and whether the inspected indicators meet the requirements of the design specification;

 

4) The use of refractory materials should be carefully investigated and understood, and whether the periodic use performance of refractory materials has been recognized by many users;

 

5) Whether the price, service life and economic benefits of refractory materials can achieve the best results;

 

6) Whether the production capacity, production equipment, inspection methods and quality assurance system of the refractory material manufacturer can meet the requirements of refractory material production;

 

7) Can you provide comprehensive technical descriptions and construction materials for refractory materials;

 

8) Whether there are professional and technical personnel for on-site construction technical guidance and supervision.

 

It is recommended that after the user purchases the refractory material, it should promptly entrust a professional inspection agency to inspect it. The refractory material user shall have a third party as an inspector to supervise the construction and installation of the refractory material, and pre-test the technical level of the installer, which will greatly Reduce future maintenance costs.

 

Zhengzhou Rongsheng

 

During construction and installation, in addition to complying with the design requirements, the oven must be baked in accordance with the heating curve provided by the refractory manufacturer. It is recommended that the power plant should strictly implement regular maintenance, generally one minor maintenance once a year and one major maintenance once every three years. A minor repair once a year is to repair the severely worn area. The boiler should minimize the number of shutdowns during operation. Multiple shutdowns and starts will cause the refractory to produce thermal shock cyclic stress fatigue and increase local cracks.

 

If permanent cracks are found during maintenance, they should be repaired in time. You can choose to use acidic high-temperature adhesive and part of the high-aluminum fine powder to mix and then repair, or you can choose to use special repair materials for repair. Pay attention to small cracks. If the cracks are not repaired in time, the cracks will continue to increase. Sometimes the ash enters the insulation layer from the cracks, and the gradual increase in the amount of ash in the cracks over time will cause the furnace wall to protrude and collapse.

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