turbine
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For diesel hydrogenation, I use a back-pressure turbine. The steam pressure in Central Asia is around 3.4 MPa, while the pressure of the low-pressure steam, that is, the back-pressure steam, is around 1.0 MPa. At present, as the back-pressure steam pressure increases, the flow rate of this steam also increases; as a result, more low-pressure steam is produced by the unit, which leads to lower energy consumption. What I would like to ask is whether the relationship between back-pressure steam pressure and its flow rate is indeed as I have observed – that is, the higher the back pressure, the more steam is produced? Thank you for your guidance
When the work that needs to be done remains constant, more energy is required; therefore, as the back pressure increases, more steam is consumed
The increase in steam production is illustrated using an example of the change in enthalpy as steam does work through a turbine. 1. Assumption: The inlet pressure/temperature are 3.4 MPa/400°C, corresponding to an enthalpy of 3224 kJ/kg； The turbine efficiency remains at 88%, and its power stays at 2000 KW. 2. When the back pressure is 1.0 MPa, the enthalpy of the steam exiting the turbine is 2945 kJ/kg; the amount of steam consumed is approximately 25.81 t/h. The enthalpy difference compared to the inlet conditions is 279 kJ/kg. Converting this heat value into power gives: 279 * 25.84 = 7200 MJ/h, which corresponds to 2000 KW. 3. When the back pressure is 1.2 MPa, the enthalpy of the steam exiting the turbine is 2982 kJ/kg; the amount of steam consumed is approximately 29.73 t/h. The enthalpy difference compared to the inlet conditions is 242 kJ/kg. Converting this heat value into power gives: 242 * 29.73 = 7195 MJ/h, which corresponds to 1999 KW. 4. From these estimates, it can be seen that, with all other conditions remaining constant, increasing the back pressure leads to increased steam consumption by the turbine, and it does not allow for better utilization of high-quality steam. For the low-pressure steam in the system, this results in more low-quality steam being produced. If we consider the entire steam processing chain and look at the conditions of the waste steam emitted at the end, a different conclusion can be drawn. Therefore, the conclusion that energy consumption has decreased depends on the perspective from which it is viewed.