Installation and wear analysis of J valve of the h

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Installation and wear analysis of feeder (J valve)

Abstract: This paper analyzes and summarizes the installation and wear problems of the return valve of four 410 t/h CFB boilers in the eighth phase of the technical transformation project of Shijiazhuang thermal power plant, and accumulates experience for the construction of similar units in the future

key words: CFB boiler; Return valve; Expansion; Pouring materials; CFB boiler is characterized by its high combustion efficiency, easy to realize desulfurization in the furnace, low emission of nitrogen oxides, combustibility of inferior fuel, and a large number of solid particles circulating and Reburning in the solid particle circulation circuit composed of combustion chamber, separation mechanism and return device. It has increasingly received universal attention and rapid development from all countries. The material circulation system is an important device in CFB boiler. The working reliability of the material return valve directly affects the normal and stable operation of CFB boiler. The normal operation of the feeder during operation is the key to realize the material circulation; To reach its rated output, the boiler must ensure the balance of materials in the dilute phase zone of the furnace, so the amount of circulating ash determines the load capacity of the boiler. Therefore, during the installation of the feeder, the accuracy of the air supply angle, air volume and pressure measuring points of each air supply pipe should be ensured to realize the good fluidization of the materials of the whole feeder; At the same time, the construction quality of lining wear-resistant and fire-resistant pouring material is also one of the key issues to ensure the normal operation of the feeder. Working principle and function of the return feeder

1 the return feeder is a device that returns the circulating materials from the low pressure area to the high pressure area. It is generally divided into mechanical type (impeller rotating type) and non mechanical type (pneumatic control type). Because the circulating materials of CFB boilers are high-temperature ash and limestone, at present, most of the non mechanical return feeders that work reliably at high temperatures, wear little and control sensitively are used. The J-shaped valve is used in the eighth phase technical transformation project of Datang Shijiazhuang thermal power plant. The bed material and ash separated by the cyclone separator flow downward through the return riser lined with refractory. This project not only makes up for the blank of aluminum alloy in chassis utilization, but also goes out to valve J, and then is sent back to the furnace by valve J. Flexible expansion joints are used between the separator and the feeder, between the feeder and the lower furnace to absorb the relative displacement between the feeder and the separator, between the feeder and the furnace during the start/stop of the boiler. The feeder has two key functions: to make the recycled bed material return to the furnace stably from the separator; Provide a seal between the negative pressure of the separator and the positive pressure of the lower combustion chamber. The return feeder realizes these functions through the material level of the return leg riser. The kinetic energy of material return is supplied by the fan of valve J. by adjusting the air distribution of the rising and falling sections of the feeder, the material is fluidized

2 several key control points for installation

2.1 installation of the expansion joint of the reclaimer

the expansion amount of the expansion joint should be left enough during the construction and pouring of materials according to the drawing design. The gap of the metal guard plate and the reserved gap after the pouring of dumbbell shaped building materials cut according to the national standard 2mm rubber test piece after the construction are completed should also be measured after the installation of the expansion joint, so as to ensure that the gap is sufficient in the cold tension state, Moreover, the welding direction of the sealing plate shall be consistent with the flow direction of the medium, and the sealing shall be good. The other two expansion joints have different functions: expansion joint 1 is stretched during boiler startup, which mainly absorbs the relative displacement between the boiler water wall and the return valve caused by the downward and bilateral expansion of the boiler water wall; Expansion joint 2 is compressed during boiler startup and mainly absorbs the relative displacement between the cyclone separator and the return valve caused by its downward expansion. During installation, attention should be paid to their expansion direction. The cold drawing should be in accordance with the design regulations, and the clearance of each part should meet the requirements of the drawing. The installation should not be reversed, so as not to affect the expansion of the equipment in operation. The expansion amount of the expansion joint shall be calculated according to the overall expansion diagram of the boiler

2.2 installation of the air nozzle of the feeder

the air nozzle of the feeder is the key to ensure the normal fluidization of the return material. The material of the nozzle is generally heat-resistant steel, so the selection of welding rods should be correct during welding. In addition, the installation angle of the nozzle should be consistent with the design to ensure the fluidization direction of the material. Before ignition, ensure that the inflation port is unblocked. If the inflation port is blocked during operation, use high-pressure air for purging, and do not dredge it by mechanical methods (such as sticks)

2.3 installation of the cylinder wall of the feeder

special attention should be paid to the material of the cylinder wall equipment, the welding rod used in the installation should be correct, and the welding requirements should meet the design requirements. Due to the micro positive pressure in the feeder, the quality of metal welding is also the fundamental guarantee of tight sealing

2.4 construction of wear-resistant and fire-resistant pouring materials

in order to reduce the wear of materials to metals, wear-resistant and fire-resistant pouring materials and thermal insulation pouring materials are generally arranged inside the feeder. The falling of pouring materials will cause poor fluidization of the feeder and affect the normal operation of the feeder. Therefore, the pouring material should have the properties of high compressive strength and high wear resistance coefficient. Through analysis and research, the construction method of using steel formwork in the straight pipe section and wood formwork in the elbow part is adopted to enhance the rigidity of the formwork, reduce the loss of water in the solidification process of the pouring material, and significantly improve the strength of the pouring material. In addition, the current wear-resistant pouring materials are mostly low cement materials, and the amount of water added has a great impact on the strength of pouring materials. During construction, the amount of water added should be strictly controlled according to the change of temperature. Expansion joints shall be reserved for the construction of pouring materials, with a spacing of ≤ 900 mm, so that the pouring materials can be regularly cracked when heated and expanded, and there is no cross joint, so as to prevent the pouring materials from falling off. The construction thickness of the pouring material is biased to better meet the growing functional needs of our customers. The difference should be guaranteed within the allowable range, so as not to affect the output of the feeder. Wear analysis of the return feeder

3 the wear of the return feeder is mainly manifested in the wear-resistant and fire-resistant pouring material itself, and the severely worn parts are the elbow of the return pipe, the return port and the surrounding of the obstacles. There are four main forces on the materials in contact with the plastic part shape materials in the reclaimer and the actual shrinkage rate of the pouring in the forming process: its own gravity, the friction between the materials, the driving force of the air flow on the materials, and the friction between the materials and the pouring materials. The friction between materials and pouring materials mainly includes erosion and impact. At the elbow of the return pipe, due to the effect of gravity, a large number of materials are concentrated in the lower part of the return port, and the direction of materials will change, which intensifies the friction in this part. As the materials at the return port are affected by the rising air flow in the furnace when entering the furnace, some materials change direction (from falling to rising). Due to the unstable flow, the fly ash will cause erosion or impact friction to the furnace wall. Sometimes the material will form eddy current in this part, which will also aggravate the wear of this part. When the fly ash encounters obstacles such as pressure, pipe temperature, etc., the direction of movement will also change, resulting in diversion and serious local wear. In the valve body of the return valve, there must be a large number of materials to ensure the height of materials to achieve the sealing effect

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