Challenges with Compressor Start-up/Dry out Runs with Dissimilar MW Gases Than the Process Gases

This presentation discusses the challenges with compressor start-up/dry out runs using heavier or lighter MW gases than the actual process gas. It is very common for the end user to specify a compressor dry out case using Nitrogen, Hydrogen, air or a gas mix. Sometimes, it is challenging to accommodate these dry out cases due to significant volume mismatch between the process gases and dry out gas. These dry out runs also poses challenges with respect to maximum allowable working temperature (MAWT), control system design, ease of use by the operator in the field and the driven equipment and driver configurations.

In this presentation, the authors discuss the theory behind the volume mismatch and strategies to implement these dry out cases. The authors also discuss various compressor configurations such as back-to-back, extraction, speed changes, decoupling parts of string and independent control loops etc. which may provide an economically viable solution to solve the dry out run problems. The presentation also covers the considerations for dry gas seal mechanical design, control system design and ease of operator to run the start-up case in filed. Finally, the authors presents a case study where one these above strategies was successfully implemented.