【Special Topic】Water System in Coal Gasification Process
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This post was last edited by Jiang Chengzi on 2009-5-15 at 22:00. In coal slurry preparation and gasification processes (Texaco, four-nozzle type), water is utilized in various ways; please discuss their water systems (the use of water as well as the generation and treatment of wastewater). Participate more – participation brings rewards!
Let me start. In coal slurry preparation, the wastewater from the production system can be used to replace fresh water or water of better quality for grinding coal, which helps to treat the wastewater to some extent and reduces the consumption of fresh water at the same time； The water used for replenishment or deoxygenation in the gasification system can be the condensed liquid from the purification system or the hydrolyzed liquid from the urea process, which helps to reduce the amount of desalinated water required to a certain extent.
Most of the water used for slurry preparation in our plant comes from distilled wastewater, to replace raw water. However, when using distilled water, attention must be paid to the temperature of the grinding water, as a high temperature can affect the temperature and viscosity of the coal slurry. The condensate from the gasification conversion process replaces the water added to the carbon column trays, serving as a substitute for the boiler feedwater. Make full use of water in the system by collecting water such as the overflow from the lock hopper flushing tanks and adding it to the preheating tank.
The water used for slurry preparation in our plant is mainly the filtrate from the filter, the water used to wash the filter cloth, and methanol waste liquid； Deoxygenated water is made from the low-temperature shift condensate and primary water from the shift process, while heating is provided by high-pressure flash vapor. The mechanical seal water for pumps such as slag sump pumps is made from graywater.
Used for coal slurry preparation: a small amount of raw water, filtrate from the filter press, seal water for vacuum pumps, and wastewater from low-temperature methanol washing. Used for system replenishment: low-pressure condensate is used to replenish the deoxidation tank, while high-pressure condensate and a small amount of BW are used to replenish the scrubber tower. The system generates approximately 60 tons of wastewater per hour; ammonia nitrogen is removed through alkaline stripping, and part of this wastewater is sent to the coal storage area and for use in power generation equipment.
The most important aspect of the water vaporization system is to properly control calcium and magnesium ions, as well as suspended solids, in the graywater, in order to prevent scaling in the pipes
NH3-N and COD in graywater are also factors that affect water quality. While striving to save water, it is necessary to enhance the capacity for biochemical treatment, and it is also important to add some raw water to improve the water quality.
To use water systems in a rational and optimized manner, it is necessary to consider the entire process system as a whole. On one hand, we must ensure rational use of water at the local level, while also taking into account the comprehensive utilization of water on an overall scale. For example, using methanol wastewater or other types of sewage in coal grinding mills, or sending purification and conversion condensate to gasification deoxidizers are good examples. The black water from the gasification process is recycled after sedimentation; this represents a case of localized water use. We can think creatively about this topic and offer suggestions step by step.
Bro, deoxygenated water is used together with regular water – aren’t you worried about scale formation? Deoxygenated water is usually used to supplement desalinated water, right?
Returning to the previous version: the water hardness here is not high, and the diameter of the pipes through which deoxygenated water circulates in the system is also relatively large.
It is best to use deionized water for making up water in the deaerator. Although the hardness of ordinary water is not high, ions such as chloride, silicate, and iron are also detrimental to the deoxygenated water. Just my personal opinion, haha