One of the most common applications for a hogging ejector is in conjunction with a steam turbine exhaust condenser’s air venting equipment. In this application the hogging ejector is turned on at start up, greatly reducing the equipment’s start up time. The hogging ejector also helps compensate for the additional air in-leakage that will be present at start up through the turbine’s gland seals as the turbine spins up to operating speeds. Once the system has started the hogging ejector is isolated and removed from service.

Other processes that benefit from the use of a hogging ejector include many batch processes. If a vacuum system is shut down and restarted on a regular basis, as different batches of product are being processed, a hogging ejector is often used to help the system pull down faster. This can decrease a batch’s run time allowing more batches to be processed. In this way hogging ejectors can add to process efficiency, creating a positive economic impact for the user.

While hogging ejectors are great at evacuating a system at startup, there is a motive steam cost associated with operating them. They are designed to have a lot of capacity and this causes them to use a considerable amount of motive steam.  Normally this is acceptable because they are run for a short amount of time. At times equipment users will continually run a hogging ejector to gain performance. This is normally done to compensate for other issues with the main ejector system or to help offset high air in-leakage. While operating a hogger over the short term to maintain operation is acceptable, operating the hogger year round comes with a significant operating cost. An example below has been generated showing the yearly operating cost of a hogging ejector used in an air venting package.

Hogging Ejector Steam Cost

These below calculations were done assuming a steam cost of $4 per 1,000 lbs of steam, continual 24 hour a day operation, and 350 days a year accounting for outages and down time.

You can see that while the hogger only costs $11.00 in the example above to start up a system, operating it round the clock for a year costs $91,000. If the hogging ejector is being run continually, the root cause of the problem should be identified so that the hogger is not needed for continual operation. Graham field service is available to assist if expertise is needed to identify a performance problem. Making sure a system is working correctly and properly utilizing a hogger has financial implications to a user’s bottom line.