The role of protective steam in a two-stage conversion furnace

It serves to protect the air coil, especially by preventing it from overheating when there is a lack of air supply. It also prevents excessive steam from causing the temperature of the air coil to drop, thereby reducing the concentration of water and vapor in the system

1. Protect the two-stage furnace nozzle to prevent damage!

1. The start-up and shutdown shut-offs prevent the feed gas from mixing with air, thus avoiding cross-contamination. 2. Low-load protection nozzle to prevent damage! Ensure the gas exit velocity of the nozzle is at 30 m/s; 3. Increase the high variable water-to-gas ratio. Adding steam will of course lower the outlet temperature of the second-stage furnace.

One more thing: adjusting the decarburization heat load

No, it’s not used to adjust the heat load! No cheating!

Additional note: 1. Ensure the flow velocity at the nozzle； 2. To prevent the backflow of hot gas after an air interruption, although a check valve is available. Take a close look; it was mentioned on the 4th floor as well :P :P :P

It’s true. For small and medium-sized plants that use thermal potassium alkali decarburization, the heat requirement per ton of ammonia produced for decarburization is higher than that in larger plants. In order to save gas, when the carbon-to-water ratio in the first-stage furnace drops below 3.1, process air is supplemented with steam at 0.3 times the amount of natural gas used (the design value); in such cases, the heat required for decarburization is insufficient. As a result, the maximum temperature of the regenerated lean liquid reaches 123 degrees, causing a significant increase in the methanation temperature. Increasing the amount of steam supplied in the second stage normalizes the methanation temperature.

It is mainly to protect the second-stage furnace nozzle and prevent damage

Other methods can be used to adjust the decarburization heat load, such as introducing steam into the reboiler or adding steam at the high-variability inlet. Why is it necessary to adjust the steam in the two-stage furnace?

Ensure even distribution of the gas, achieve stable combustion in a two-stage furnace, protect the coil, increase the water-to-carbon ratio, enhance the decarburization heat, and prevent gas backflow

Everyone is right. 1 Protection coil 2 Protection nozzle, to ensure flow rate. 3 Prevent gas backflow; provides check function. 4 By similarly adjusting the decarburization heat load and increasing the protective steam, it is equivalent to raising the water-to-carbon ratio in the second-stage furnace as well as the steam concentration in the conversion process.

The more we discuss it, the clearer things become. However, adding steam to the air in the second-stage furnace is primarily done to protect the burners, preventing the air compressor from shutting down and avoiding backflow of process gas that could cause micro-explosions and damage the burners. Local explosions can cause severe damage to the burners. Steam still needs to be added to air burners even when they are operating at full load, which shows that it’s not a matter of “ensuring flow rate.” The heat required for decarburization can be supplied using low-pressure steam at 1111-C; there’s no need to use medium-pressure superheated steam beforehand, as that would waste the equipment’s capacity. Therefore, it’s also not about “adjusting the heat load for decarburization.” In the event that the air compressor shuts down, ammonia plants have comprehensive measures to cool the convective section. Moreover, the amount of steam added has little effect on cooling the coils, so it’s not meant to “protect the coils” either. Adding such a small amount of steam to the air has minimal impact from a process perspective; certainly there is some effect, but it’s definitely not significant enough to be considered important. I agree with HU*ANGJI's view.

Steam is introduced into the two-stage furnace primarily to protect the pure oxygen distributor, control the flow rate, prevent the backflow of flammable gases, reduce the surface temperature of the nozzles, and protect the preheater

①The flow rate of air entering the air distributor of the second-stage furnace must be sufficient to prevent the surface of the distributor nozzles from being damaged, and to ensure proper mixing with the gas from the first stage after it is ejected. According to the design requirements, it is acceptable as long as the air flow rate is not less than 45% of the normal value. When the flow rate is lower, the pressure can be reduced, or manual operation of MCV-19 can be used to add a certain amount of steam. ②Under normal conditions, MCV-19 also needs to maintain a certain mixture of steam and air to prevent backflow, that is, the flow of hot gases, in the event of a failure in the air compressor. There is a check valve at the outlet of the air compressor, but it cannot guarantee zero leakage. Therefore, it is necessary to supply a small amount of steam regularly. ③The material of the air preheating coil in the convection section is low-alloy steel, which cannot withstand the corrosion caused by high-temperature, high-pressure air. Therefore, when the air flow rate is too low and the outlet temperature of the preheater exceeds the designed maximum value, it is necessary to reduce the heat load on the convection section; in such cases, more steam is added via MCV-19. 4. If too much steam is added, the temperature of the catalyst bed in the second-stage furnace will decrease.