1. Chain belt grate. The chain belt grate is a wide circular chain belt which is surrounded by and supported on the the front and rear axles via the chain wheels. At present, ZOZEN packaged chain grate steam boiler mainly adopts the large-block chain belt grate with a capacity of 1-20 tph.
2. Scale grate. The scale grate has many advantages. The obvious one is that there is less coal leakage. The scales can be replaced without shutting down the boiler. The ventilation is balanced, and the ventilation section is relatively small (6%). The chain grate bars only bears the stress or high temperature instead of both of them, which improves the working conditions of the chain grate.
3. Beam grate. Its main feature is that the width and length of the grate can be extended in a wide range, and the tonnage of the boiler can be larger. At present, the tonnage of the domestic beam chain grate steam boiler can reach 240 tph. The grate is featured with long service life, good durability, smooth arrangement and convenient replacement.
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Already installed service pumps have little way to completely overcome the cavitation damage caused by poor pump cavities (Pump Booklet, Volume 1). This article will mainly introduce ways to reduce cavitation damage in service pumps. These methods have achieved significant results in practical applications.
First, the causes of cavitation
Cavitation is caused by the liquid vaporization, the liquid molecules escape the liquid surface, a process of gas molecules, known as "vaporization." The degree of vaporization of liquid pressure and the size of the high and low temperature. Dissolved in the liquid gas, pressure and temperature changes will be released, the formation of cavitation. When the internal pressure of the liquid drops below the saturated vapor pressure of the liquid at the temperature, bubbles or cavitation are formed in the local area. When the pressure rises, the bubble is suddenly crushed by the pressure around it, Extruded to the center of the bubble at an extremely high rate, causing a hydraulic shock to the equipment. The entire process of microbubble generation, rupture and physical and chemical effects on the overcurrent surface is called cavitation.
If the liquid does not contain any impurities, cavitation does not occur even under low pressure. Foreign cavitation researchers believe that the tensile strength of ultra-pure water (ie, the limit for generating holes) far exceeds the tensile strength of conventional metal materials. However, the usual liquid always contains gas or solid, these impurities become corrosive nuclei, under certain conditions to induce the occurrence of holes. Due to the different proportion of water and sand, the movement path of sand and streamline may speed up the occurrence of cavitation. The author describes in detail the paper "Cavitation and Anti-cavitation Materials for Mud Pumps" (Lubrication and Sealing 1993).
Second, in service pump cavitation diagnostic method
Pump users often can not use the factory flow rate of a certain drop in the head to determine cavitation occurs. In-service pump cavitation occurs, except in the cavitation damage observed after the law can be used (1) ultrasonic method; (2) pump noise method; (3) vibration method to determine.
Observation method: destruction of surface observation method is to observe the method afterwards, according to the destruction of the surface shape to judge. Due to cavitation, casting porosity, erosion, erosion, etc. will cause the metal surface shape and the ideal shape of the difference. Cavitation erosion of the metal surface is usually honeycomb, which is caused by the local high-speed water hit the metal fatigue damage the metal surface, so the honeycomb holes are generally connected with the outside, most of the pit and the metal surface perpendicular to. Loose casting defects are often hidden in the metal inside, and sometimes because of the erosion of the water inside the loose metal pores on the surface and mistaken for cavitation, but when we continue to use the mechanical approach to the surface will still find its interior still Stoma. Scour wear traces often appear with the same direction of the water groove, but pay attention to the flow sometimes vortex.
Noise method: pump noise method is relatively simple, you can not contact with the pump. However, as the noise method is greatly affected by ambient noise, it shows the highest intensity. The general pump cavitation has reached a very strong stage, when the human ear has been through a strong cavitation crack sound discrimination cavitation conditions. Therefore, the pump body noise method is not suitable for on-site monitoring of cavitation.
Vibration method: This method is through the accelerometer probe pump vibration frequency of a method, the method is simple, but the sensitivity is low. Especially for large pumps, pump body stiffness. The partial cavitation caused by the pump bubble rupture caused by the vibration response slow, at the same time, pump more vibration source. Vibrations due to cavitation are often masked by other vibrations. Therefore, the vibration method is only suitable as an aid to on-site monitoring of cavitation.
Ultrasonic method: Ultrasonic method of measuring cavitation is simple, convenient debugging, and free from the interference of other environmental noises, and is very sensitive to the occurrence and development of cavitation. Therefore, as a pumping station to monitor cavitation is a more ideal way.
In addition, Fushun Petroleum Institute of Chemical Machinery Zhao Huijun introduced the use of electricity to predict cavitation centrifugal pump performance ("Journal of Petrochemical Industry" 1997). 
The chain grate is the combustion equipment of coal-fired steam boiler. There are three main types and structures: chain belt grate, scale grate and beam grate.
Cavitation is one of the common faults in hydraulic machinery. Due to the unreasonable design of inlet pool or pipeline and the incomplete consideration of atmospheric pressure, temperature, and the change of gasification pressure of the medium, the pump often fails due to cavitation.