Transformation operation and steam addition

The main role of the steam added in the shift section is to react with CO to produce hydrogen and CO2; it is used primarily to increase the water content in the process gas, especially in situations where the water content in natural gas, oil, as well as the gas produced by certain atmospheric vaporization and coal gasification processes is low. The amount of steam added is determined by the requirements of the shift process, and generally, an excess amount of steam is used.

The amount of steam added is related to factors such as the conversion rate, catalyst performance, and the reaction temperature in the catalyst bed. When the conversion rate decreases and the CO content in the converted gas increases, the amount of steam added should be increased appropriately. When the catalyst’s active temperature is low, the operating temperature is also low, and the amount of steam added can be appropriately reduced. Conversely, the steam volume should be increased appropriately. When the hydrogen sulfide content in the gas is high, the amount of steam added can be increased accordingly. When the load, system pressure, steam pressure, temperature of the semi-water gas at the outlet of the saturated tower, and the oxygen content in the semi-water gas change, it will cause variations in the bed temperature; therefore, the amount of steam supplied must be adjusted accordingly to maintain a stable bed temperature. In production, adjusting the amount of steam added is the primary method for controlling the temperature of the shift converter. Reducing steam consumption is of great significance for lowering consumption metrics and saving energy. Therefore, while ensuring that the conversion rate meets the requirements, steam should be used as little as possible, and auxiliary lines should be employed to regulate the bed temperature in order to save steam consumption.

Measures to reduce steam consumption in the conversion system include 1. using low-temperature, high-activity catalysts to decrease the gas-to-wet semi-water gas ratio fed into the conversion furnace. Experiments have shown that to achieve the same conversion rate, the higher the reaction temperature, the higher the required steam ratio; therefore, using a catalyst with low temperature and high activity can reduce the steam-to-gas ratio fed into the furnace, thereby saving steam. 2. Increase the temperature and saturation of the semi-coke gas at the outlet of the saturated tower. Typically, depending on the temperature of the semi-water gas at the outlet of the saturated tower, the tower can recover 1.0–1.5 tons of steam per ton of ammonia. The higher the outlet temperature, the more steam can be recovered; therefore, the temperature of the semi-coke gas at the outlet of the saturation tower should be increased as much as possible. To this end, there should be a tower diameter and height, as well as a packing area that meet the production requirements, efficient packing, and an appropriate hot water circulation volume. 3. Improve temperature regulation and heat recovery between converter sections to make rational use of heat. The transformation reaction is an exothermic reaction, and heat must be continuously removed during the reaction process. The medium-transformer furnace uses water spray cooling to remove heat. The condensed water or deionized water sprayed is vaporized inside the furnace, which not only serves to regulate the temperature of the catalyst bed and remove heat, but also increases the water vapor content in the gas entering the lower catalyst bed, thereby saving external steam supply. 4. Improve the insulation of equipment and pipelines to reduce heat loss.

The effect of steam-to-gas ratio on the CO conversion reaction: The steam-to-gas ratio refers to the volume ratio of steam entering the conversion furnace to the CO in the gas. (It can also be expressed as the volume ratio of water vapor to dry semi-water gas.) The gas ratio has a significant impact on the CO conversion rate. The CO equilibrium conversion rate increases as the steam-to-gas ratio rises, but this increase is initially rapid before slowing down. That is, when the steam-to-gas ratio is low, the slope of the CO conversion rate curve is high; as the steam-to-gas ratio increases, the slope of this curve gradually decreases, and once the ratio reaches a certain value, the CO equilibrium conversion rate curve tends to become flatter. The effect of gas-to-gas ratio on reaction rate. Generally, when the gas ratio is low, the reaction rate increases rapidly as the gas ratio rises; thereafter, it gradually decreases as the gas ratio continues to increase, a pattern similar to that of the effect of the gas ratio on the equilibrium conversion rate of CO. Therefore, at lower steam-to-gas ratios, appropriately increasing the steam-to-gas ratio is beneficial for improving both the CO conversion rate and the reaction rate; however, an excessively high steam-to-gas ratio is not economically viable.

The transformation process is different, so the methods of operation are also different. Even for the same process, the operations may vary from one system to another. It is related to a series of factors such as the use of catalysts. Therefore, it is required that operators use their brains and hands skillfully during the operation process; more importantly, they need to be good at summarizing in order to optimize the operations. For example, how much air volume and how much steam should be added, what the scale of hot water circulation should be (using a saturated hot water tower for conversion), how many times the bypass line should be opened or closed. It is necessary to pay close attention and draw conclusions during normal operation in order to understand the patterns involved, which will make things easier to handle; it is possible to determine immediately if too much or too little steam has been added.

The amount of steam added is primarily related to the operating temperature of the catalyst, the temperature of the semi-water gas at the outlet of the saturated tower, the oxygen content, and the composition of the gas fed into the system

In the case of low-temperature conversion, it is necessary to take into account the vapor pressure to prevent excessive pressure, which could lead to vapor condensation at that temperature; generally, it is required that the saturation temperature at this pressure be 20 degrees lower than the operating temperature. 7# YAODI2007