Washing tower drainage issues during the initial startup of gasification
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At the initial stage of startup, the system pressure in the gasification unit is very low; at this time, the wastewater from the gasification furnace is directed to the vacuum flash drum (it may also be sent to the startup heat exchanger, and after heat exchange it goes into the sedimentation tank). Once the system pressure rises above 1.0 MPa, the wastewater from the gasification furnace is routed to the high-flash tank. However, during startup, the wastewater from the scrubber becomes a problem. Since the scrubber is installed almost at ground level, at a higher position than both the high-flash and low-flash drums, most plants choose not to discharge water until the system pressure has risen enough at the beginning of gasification. But not discharging water can lead to blockages in the scrubber’s drainage pipes. Some plants decide to discharge the water from the scrubber on-site during startup, and then close the drain valve afterward to send the water to the high-flash tank. Other plants install an additional pipeline from the scrubber’s drainage system that leads to the slag tank, so that the water from the scrubber can be sent to the slag tank during the initial stages of operation. Yet this approach also presents problems, as the temperature of the water from the scrubber is high, which can cause cavitation in the pumps used in the slag tank. Some people suggest directing the wastewater from the scrubber to the vacuum flash drum, as this drum operates under negative pressure, creating a pressure difference with the scrubber. Although the heights of the vacuum flash drum and the scrubber are almost the same, the resistance in the pipelines connecting these two units is relatively high. It remains to be seen whether this approach is feasible; I hope everyone will share their opinions and insights! See if there is a better way to allow the scrubber tower to discharge water properly even when there is no pressure in the system.
Our company discharges the fluid into a slag tank; the saturation temperature at 1.0 Mpa is 118°C. The slag tank operates at atmospheric pressure, so discharging there is equivalent to flash evaporation. Therefore, cavitation in the slag tank pump does not occur.
Your logic is incorrect, right? The saturation temperature at 1.0 MPa should be 184°C. When water is sent to the slag pool and flash-evaporated, it becomes water at atmospheric pressure; this water is then heated to the saturation temperature corresponding to atmospheric pressure, which is 100°C. Wouldn’t that make cavitation more likely? Sludge pool pumps are prone to cavitation at 80°C, let alone at 100°C.
I’m a beginner and I want to know what kind of burner you use – four-channel? ? Is it a water-cooled wall gasifier? ? ? Mutual learning*
Ours is a three-channel internal mixing burner, a furnace with refractory bricks, not one with water-cooled walls
Just after adding the material, the water temperature won’t rise that quickly; there’s always a process of heat accumulation
We also often encounter this problem: at the beginning of operation, the wastewater from the scrubber cannot be discharged, so we have to increase the pressure slightly to speed up the process. By the time we finish adding the materials, the pressure already reaches almost 5 kilograms; we then switch to draining water, and after that the pressure drops to around 10 kilograms. Once we switch to high-flash mode, there are no more issues
What type of furnace do you have? . . .
Texaco water-coal slurry gasifier, refractory brick inner wall, quenching process.
In the initial stage, the water from the scrubber tower is discharged to the true flash point (it is essential to ensure that this pipeline is unobstructed before starting up). After the materials have been added, the pressure is quickly increased to above 1.0 MPa, and the water flow is directed to the high flash point.
Plant 3 has a design in which the scrubber tower discharges black water to the true flash tank, using hard-sealed ball valves along with blind flanges; however, this increases the workload during operation. In our project design, there is high-pressure boiler feed water with backflow; this design is excellent as it effectively solves the problem of inevitable blockages at the bottom of the scrubber tower.