Our topic for this month is going to focus on the various factors that impact an ejector’s motive steam consumption rate. It’s also going to explain how to calculate the motive steam consumption for an ejector, which is needed when calculating a system’s utilities cost.
Motive steam is critical to an ejector’s performance and making sure an ejector has enough motive steam is important for successful operation. Additional motive beyond the ejector’s design will not add additional ejector load capacity, however it may be useful if the ejector’s discharge pressure is above design. If this is not the case, then the system will be wasting steam. Knowing how to calculate an ejector’s steam consumption can be used to make sure that excessive steam is not being wasted.
Ejectors require energy in the form of motive to do their work of compression. While there are various different types of fluid that can be used as an ejector’s motive supply, steam is by far the most common due to its availability. The motive steam is delivered to an ejector via the ejector’s motive nozzle. As the steam passes through the nozzle, its potential energy is converted into kinetic energy. That energy is what drives the ejector. If the motive steam flow is too low, the ejector will lack the energy required to maintain its internal shockwave and the vacuum will break operation and significantly degrade.