Reasons for vibration in the lockbox flushing water pipeline and improvement suggestions

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Our company’s gasification unit employs the clean water coal slurry gasification technology developed by the Northwest Research Institute for multi-slurry gasification. The slag and water resulting from the gasification process are discharged intermittently through a hopper system, which operates using a cycle of pressurization, slag collection, pressure release, slag discharge, and flushing – a pattern similar to that used in gasification units of the same type in China. Since the lockhopper system operates intermittently, the vibration of the lockhopper flushing pipeline is also intermittent. Vibrations in the pipelines can cause the accessories of control valves to fall off, bolts to break, and the welds in the pipelines to crack, thereby creating significant safety hazards and risks for the installation. Based on long-term operational testing, the following conclusions have been drawn. http://www.smjqh.com/d/file/zcxdth/wenti/2015-11-17/f6504cf271282a0b0724a43a58a848e0.jpg 1. Reasons for vibration in the water supply pipeline. The lockout/tagout system is set to cycle once every 30 minutes; the flushing water valve is opened and closed every 30 minutes, resulting in approximately 48–49 operations per day. Vibration mainly occurs in the pipeline where the flushing water valve is located. Due to the short length of the pipeline and few bends, the use of flexible connectors has little effect. When the flushing water valve is opened, the difference in liquid level in the flushing water tank causes the rocker of the check valve to strike the valve cover violently, thereby generating vibration in the pipeline. When slag discharging from the lock hopper is completed, the slag discharge valve KV1303 is closed, turning the lock hopper into a sealed container. Water from the flushing pipeline continues to flow into the lock hopper; these two streams of water meet, creating a water hammer effect that impacts the pipe at the flushing valve KV1304, causing the check valve’s core to be pushed back forcefully. Three impact vibrations occur during one slag discharge process. II. Measures to control vibration and renovation suggestions. First, control of the vibration source. The source of vibration is the short-term change in the flow velocity and direction of the fluid inside the pipeline, which leads to water hammer vibrations in the pipeline. Methods for altering this source of vibration exist. The first is to change the structural properties of the valve itself (a quick-opening ball valve is used here). Such as valve cores, flow channels, etc. The second is to change the valve operation state. The method of altering the vibration source by changing the structural properties of the valve itself can fundamentally solve the vibrations caused by valve opening and closing, but it is extremely costly, and it is not possible to accurately predict the effects of making such changes to the valve; therefore, it is not recommended. Changing the operating state of the valve is achieved by adjusting the timing of the sequential control program for the lock hopper; this allows the flushing valve and the slag discharge valve to open and close slowly, thereby preventing vibrations caused by sudden changes in the fluid flow. Since the slag discharge valve KV1303 is closed after normal slag discharge from the lock hopper, the flushing water generates strong water hammer effects due to inertia. By eliminating these water hammer effects, it is possible to keep the pressure relief valve open during the slag discharge process. This method is simple and feasible. Secondly, there is a change in the flushing water pipeline design; by altering the pipeline, it is possible to change the frequency at which water hammer occurs, thereby breaking the resonance between the water flow and the pipeline. Expansion joints and spring supports are used to further reduce vibrations in the flushing water pipeline. Third, appropriately extend the time for the valve to close, using the air resistance from the instrument air source to control a slow closure of the valve.