Discussion on the Reuse of Low-Pressure Steam Generated as a Byproduct of Carbon Dioxide-Stripped Urea Production
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Hello, colleagues. I would like to seek your advice and discuss the following: as for the carbon dioxide stripping of urea process, how is the excess low-pressure steam generated (with a pressure of around 0.36 MPa) recovered and utilized? We have three sets of traditional carbon dioxide stripping urea plants here, all of which are operating at full capacity. The low-pressure steam generated as a by-product is used to heat the first-stage evaporator, the distillation column heaters, the booster, and the stripping system. There is also some excess steam, around 6–8 tons per hour, which is currently being vented. Several options were also considered: one is to use circulating water for cooling and then replenish it as circulating water ； Second is to enhance the operation of the low-pressure deaerator ； Third is the use of lithium bromide technology. These various options have their advantages and disadvantages. How is the vent steam from everyone’s installations handled? Let’s exchange ideas. We can also discuss how new technologies in this field are currently being developed.
The first option is completely unfeasible: steam condensation releases heat, while the evaporation of circulating water absorbs heat; one ton of the former corresponds to almost one ton of the latter, which is roughly equivalent to simply releasing that heat into the atmosphere； Article 2 poses safety risks, as the quality of the steam may not be guaranteed. Article 3: It is suitable for use when there is a need for chilled water, or for cooling or heating buildings, etc
The first point is mainly considered from the perspective of water conservation, with little attention paid to energy consumption issues. In an environment with a shortage of water resources, this is not entirely unacceptable.
Recycling of water vapor pipeline networks
1. When used in conjunction with an air separation unit, a preheating heat exchanger is added in front of the heater during the regeneration of the molecular sieves in the air separation unit; by utilizing this heat, the amount of steam required at 1.3 Mpa (or 2.0 Mpa) can be reduced. Before adopting this solution, it is necessary to take into account the adjustments available in your facility’s steam network system. Advantages: It is best to have a extraction-condensing unit; by adding an extraction condenser, the boiler load can be slightly reduced. . Disadvantage: In practice, multiple positions need to work together, and it is difficult to coordinate unified command for execution. . . 2. Connect the previous small generator to the power grid for power generation; the high-voltage level in this case might be a problem, but 380V low-voltage should not pose any issues. .
This portion of steam can indeed be utilized in this way: since the distance between the various stations is too great, and the steam pipelines are used intermittently, the saturated steam contains a large amount of water, which makes it more difficult to make adjustments between the stations. The main issue is that the quality of the by-product steam is too low, its quantity is limited, and its utility value is not high.
Renovation of the carbon dioxide compressor turbine: a steam injection system is designed to allow the steam to return to the turbine for use, thereby reducing the need for fresh high-pressure steam and lowering the amount of steam generated by the boiler. However… . The energy-saving effect should be around 90 per ton of steam at present? 90×7×8000=5 million per year. . Upon calculation, it might be appropriate to replace the turbine; P
1) Used for cooling chilled water in summer； Used for heating in winter ； 2) Use a steam-jet heat pump to raise the pressure to 6~8 barG.