Ash discharge from SHELL furnaces

In a Shell furnace, the syngas carries fly ash upward, while the molten slag moves downward along the cold walls due to gravity. Cooling is achieved through spraying and a slag pool; the non-filtrated glass slag enters the hopper along with the water flow via a collection tank. It’s a very simple process

The gasification slag treatment system is responsible for cooling the slag from the slag discharge device, crushing it into particles, and discharging it. The slag tank is located at the bottom of the gasification furnace shell, and annular nozzles are installed at the top of the slag tank to spray continuously. Ring nozzles are installed to wet the fly ash and unburned coal dust, thereby carrying them into the slag pool. When the slag falls into the pool, it solidifies and breaks into small particles. In the channel through which the slag is discharged to the slag collector, any remaining slag lumps are crushed in crusher X-1401. To prevent large slag particles from entering the water circulation system, the water supplied to the annular nozzles is drawn from the top of the slag collector V-1402. The water circulation creates a downward flow within the slag tank, and this flow helps to carry the slag from the tank toward the slag collector. Due to the composition of the slag, it flows freely from the slag discharger into the slag pool, causing the slag streams/droplets to break apart upon impact with the surface of cold water (quenching). The slag can be easily conveyed and discharged from the system through the slag removal system. During abnormal operation, large slag clumps may form; when these hit the water surface, they do not break completely. Once they reach a certain size, it can lead to problems with slag discharge. To address these issues, a mechanical slag breaker is installed between the slag pool and the slag collector. To prevent the accumulation of solid particles and excessive erosion in the circulation loop, the water circulation is controlled separately from the operating conditions at a fixed flow rate. Coolers (E-1401A/B) are installed in the slag pool water circulation loop to remove the heat used to cool the hot slag. To maintain a sufficiently low solid content in the circulating water, a portion of the water containing solids is discharged to the preliminary water treatment system via a hydrocyclone; this lost water is replenished by high-pressure circulating water free of solids, through control of the sludge tank level. Slag pool level control provides low-low and high-high level emergency action outcomes for the gasifier trip, closure of all emergency valves around the slag pool, and circulation pump trip. The low–low liquid level interlock is designed to prevent syngas from passing through the slag collector, while the high–high liquid level interlock serves to protect the walls of the slag tank and the slag plug discharge device. Coarse materials (particle size > 250 μm) are discharged from the dewatering bin via a chain slag skimmer and conveyor belt. The water containing fine particles – a mixture of slag fines and unburned coal – is pumped to the separator/settling tank of the U-1700 unit. The solids are removed as a filter cake and returned to the raw coal system, where they are sent back to the gasifier together with the raw coal. The remaining water is reused in the slag removal system. The design of this system is based on DEMROLEC’s experience. The diameter of all slag discharge valves is 12". Since the water in the slag pool system comes into direct contact with the syngas, trace amounts of components in the syngas will be absorbed. The designed sequential discharge procedure minimizes the discharge of polluted water. However, the discharge of polluted water cannot be completely ruled out; for this reason, the depressurized exhaust gas is sent to the flare system. Some slight odors can be detected near the dehydrating chamber.

The slag pool and the vaporization furnace are integrated; at the bottom, water at 45 degrees is introduced to cool it down, and then the slag is removed through a slag collection and discharge system

The lower part of the SHELL gasifier collects most of the slag through a quenching process. In addition, some of the ash carried by the syngas is collected using high-temperature ceramic filters, while venturi washing and wet scrubbing towers are employed to remove trace amounts of ash from the syngas. The solid particles in the graywater and blackwater are removed in Unit 17 through flocculation and sedimentation. Therefore, the ash slag is obtained in three parts, namely wet slag, dry ash, and filter cake.