Why are there necks at the outlet of gasifiers?

Is the necking of the gasifier designed to match the downcomer?

Dude, when you mention the necking of the vaporization furnace, do you mean the junction between the combustion chamber and the quenching chamber? If it is for the laying of the combustion chamber bricks, then the bricks for the combustion chamber can be laid; otherwise, it is not possible to lay those bricks. This post was last edited by xuqinger on 2009-3-6 19:11]

1. The design of the reaction section in the furnace must meet the requirement of low flow rates for the reaction residence time; therefore, it has slightly larger dimensions, whether circular or square in shape. 2. The design of the furnace outlet only needs to meet the requirements regarding material flux, pipeline flow rates, and manufacturing costs. 3. Designing the outlet of the gasifier with a tapered connection can significantly reduce manufacturing complexity, costs, and investment; it also helps to meet the material flux requirements while eliminating unnecessary elements. Experts, please share your opinions

A pressure vessel must be formed, so of course there will be a neck! To ensure the necessary flow rate of the material, the gasification furnace has a constriction! Maybe the original poster meant that the location of the shrinkage is not fixed!

I’m referring to the connection point between the vaporization furnace and the quench chamber; thanks for the explanation :)

Taking the Texaco water-coal slurry gasifier as an example, the addition of a neck is mainly based on the following considerations: 1. The need for heat insulation. By increasing the necking, the heat of reaction in the gasification chamber is less likely to dissipate, which helps to maintain the reaction temperature in the chamber above the ash fusion point of the slag, thereby preserving the fluidity of the slag and reducing oxygen consumption ； 2. It facilitates slag discharge. The ratio of the cross-sectional area of the slag discharge port to that of the gasification chamber is 0.1. The water-coal slurry sprayed from the top, after reacting, causes most of the resulting slag to be directed toward the conical bottom of the gasification chamber; there it collects and then flows down along the wall of the conical bottom. Thus, this narrowing portion serves to collect the slag ； 3. Control the flow rate of the gas at the outlet. The flow rate of the gas exiting the vaporization chamber is adjusted by increasing the constriction; the smaller the constriction, the higher the flow rate ； 4. Reduce equipment investment. By increasing the necking, the area of the subsequent equipment that comes into contact with high-temperature slag and high-temperature gases is **reduced**, and the amount of high-grade materials required also decreases significantly, thereby reducing equipment costs. Just my opinion; feel free to criticize.

May I ask: Why do those pipes often have changes in diameter?

Sometimes it is due to the design requirements of the system’s core components