Why is the superheating section of the heat exchanger in the Shell gasifier located in the middle of the heat exchanger?
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Why is the superheating section of the heat exchanger in a Shell gasifier located in the middle of the heat exchanger, rather than in a location higher up in the furnace where the temperature is higher?
Given that the temperature of the superheated steam often fails to meet the requirements, it is worth considering locating the superheating section in a location higher up in the furnace where the temperature is higher. This is also an area that needs improvement in Shell furnaces.
The current position represents the frontmost point and the highest temperature achievable in the acceptable process flow. Unless the problem of slagging and fouling caused by molten fly ash can be solved at low cost technically, gas-phase quenching and conduits can be eliminated; this should represent a revolutionary technological advancement
In fact, if one pays a little attention, it can be seen that the superheating section of the Shell powder gasifier is located relatively high up in the syngas cooler. After being quenched, the crude syngas enters the syngas cooler where a flow reversal occurs – that is, its direction of flow changes from upward to downward. Therefore, a gas reversal chamber is necessary to allow the crude syngas to change direction. If the superheating section were placed directly here, the tendency for scaling would be even greater, as the flow velocity of the crude syngas slows down when it changes direction, making it easier for the viscous fly ash contained in the syngas to cool down and deposit on the cross supports of the superheating section； One thing to keep in mind is that if the superheating section is indeed placed at the upper part, the temperature of the superheated steam will increase significantly. One reason for this is that the temperature of the crude syngas is higher than it is at present; another reason is that turbulent flow may occur when the high-speed crude syngas changes direction. This enhances the heat exchange effect in the superheating section, thereby increasing the temperature of the superheated steam! ! !
The location of the superheating section is determined by SEG, the design firm for the SHELL gasifier, through calculations based on the amount of saturated steam generated, the temperature to which superheating is required, as well as the flow rate and temperature of the syngas. Since a large amount of heat is needed for the vaporization of water, the high-temperature zone should be the vaporization section. The superheated steam temperature cannot be achieved, mainly because: 1. The gasification load is insufficient. 2. Ash accumulation in the superheating section results in poor heat exchange efficiency.
Why is the superheating section of the heat exchanger in a Shell gasifier located in the middle of the heat exchanger, rather than in a location higher up in the furnace where the temperature is higher? Answer: It’s not possible to put it later: lol. It shouldn’t be placed in a place with higher temperatures. I think the main concern is related to the material; it’s not that it’s impossible to do, but the cost would be too high.
In Shell gasifiers, 55 kilograms of medium-pressure steam is superheated to 400°C; therefore, the inlet temperature of the raw coal gas does not need to be very high. If the superheating section is located directly above the gasifier, the superheater must come into direct contact with the high-temperature raw coal gas at 800–900°C, which requires that the material of the superheater be capable of withstanding temperatures of at least 800°C. However, when the steam generator is placed directly above the gasifier, this problem does not arise. This is because the heat of vaporization of water is relatively high, resulting in a much faster heat transfer rate on the water side compared to the gas side. As a result, the wall temperature of the heat exchange tubes remains close to that of the water side, and it does not exceed 500°C, so ordinary stainless steel is sufficient for this purpose. The superheater involves gas-to-gas heat transfer, and the heat transfer rate on the steam side is only slightly higher than that on the raw gas side; as a result, the tube wall temperature is much higher than that in the steam generator. Naturally, the requirements regarding the material used are therefore quite stringent. I believe this is the main reason.
I passed by and learned about it; I don’t know who’s right and who’s wrong, or who has the upper hand.
Our superheated steam is generally not used for heat exchange; it serves only as power for the turbine, while saturated steam is used in heat exchangers. In other words, the superheated steam only needs to meet the operational requirements of 400 degrees and 55 bar. Moreover, the higher the temperature and pressure, the greater the demands on the equipment and the higher the costs. We need to take into account the process requirements while also striving for optimal costs and maximum efficiency. My personal opinion, thank you.
Superheaters are generally installed in the areas with the highest temperatures. Controls the superheater temperature.