Gas-cooled quenching system and waste boiler system
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Quenching system: The gas passes through quenching water for cooling----water vapor is evaporated----Venturi tube----washing tower----syngas. Waste heat recovery system: The gas goes through multiple stages of waste heat recovery units to extract heat----high and medium pressure steam is generated----Venturi tube----washing tower----syngas. I am familiar with waste heat recovery systems, but I don’t understand the quenching system. The information states that the syngas in the quenching system contains a high level of water vapor; a large amount of steam is generated during the quenching process. However, in a water-based system, this steam must be condensed. Is it because the washing temperature is high that the vapor pressure is also high? If the washing temperature and pressure are the same for both cases, is the water vapor content in the syngas the same? Could someone with more experience please explain the main differences between the two? What exactly is a quenching system? Why is the water vapor content an issue?
Quenching involves bringing the high-temperature crude syngas into direct contact with water to cool it down; a large amount of heat is used to generate steam, which is carried away along with the syngas. Due to the high content of steam in the gas, the vapor-to-gas ratio is high. If the temperature and pressure are the same after washing, the vapor-to-gas ratio is theoretically the same, because the raw gas reaches saturation and the steam partial pressure corresponds to the steam pressure at that saturation temperature.
The quenching process and the waste boiler process mentioned above are both used in projects involving water-coal slurry fluidized-bed gasification. The vapor content in the gas exiting the gasifier is related to the concentration of the water-coal slurry and the gasification temperature; if the concentration of the coal slurry and the gasification temperature remain relatively constant, the vapor content in the crude syngas discharged from the gasifier will be the same. In the quenching process, a large amount of quench water is used in the quenching section of the gasifier to cool the high-temperature syngas. Due to the high temperature of the syngas, a significant amount of water evaporates, increasing the water vapor content in the syngas. Generally, the temperature of the syngas after quenching is around 260 degrees Celsius. The syngas exiting the quenching section is then washed in a carbon washing tower. In the waste boiler process, the syngas first passes through the waste boiler to have its temperature reduced, and then it is washed. The heat from the syngas is removed in the waste heat exchanger, so less water vapor evaporates during the washing process. The high water vapor content in the syngas mentioned above should refer to the section from the quenching stage to the washing stage. If the temperature and pressure after washing are below 200 degrees, then, relatively speaking, the water vapor content in the syngas is the same under these two process conditions. Furthermore, the high vapor content in the quenching process, as often mentioned, is generally compared to that in dry gasification, indicating that dry gasification has a higher efficiency than coal water slurry gasification.
Thank you, ah, it was said in dry language. The information on the two-stage gasification process at Xi’an Thermal Engineering states that the cold extraction process can be used for methanol synthesis, which increases the water content in the gas. And the waste pot process can also be used in this technique.
A few additional points: 1. The quenching process generally consists of a quenching chamber, a Venturi tube, and a carbon black washing tower. The heat from the gas is absorbed through the vaporization of water; the ash and slag mix with the water, and the gas phase contains a large amount of water vapor (~50%), which is beneficial for the subsequent conversion stages. 2. The waste boiler process generally consists of one or multiple stages of waste boilers, dry cleaning, and wet cleaning for dust removal. The heat of the gas generates high-pressure and medium-pressure steam; ash and slag mix with water, and the gas phase contains a small amount of water vapor (depending on the operating pressure; at 3.0 MPa, the syngas contains 14% water vapor). The specific process to be chosen depends on the requirements of the product (hydrogen production, ammonia synthesis, methanol, coal-to-oil, city gas, power generation).
The quenching process generally consists of a quenching chamber, a venturi, and a carbon black washing tower. The heat from the gas is absorbed through the vaporization of water; the ash and slag mix with the water, and the gas phase contains a large amount of water vapor (~50%), which is advantageous for the subsequent conversion stages. Does gas containing 50% vapor still need to pass through a washing tower? Will a large amount of steam condense in this way?
As a supplementary note, the syngas exiting the carbon black washing tower in the quenching process contains approximately <60% water vapor. The water vapor ratio is around 1.45.
Why hasn’t anyone discussed the SHELL gasifier? The gasification efficiency of SHELL is very high; it’s much better than that of many other gasifiers, and its technology is also quite advanced. Everyone should also discuss SHELL’s quenching process. In the SHELL system, coal powder is burned in the gasifier (quenching is achieved by circulating the crude syngas back to the gasifier). The combustion gases then pass through the conduction section, the reverse chamber, and the SGC, where they exchange heat with the water in the steam drum. After that, they proceed to the dry ash removal unit, wet washing stage, shift reaction, methanol washing, and PSA process to produce hydrogen. The purity of hydrogen can reach 99.5%. Everyone, see, SHELL is still much better, right!