Automatic steam-load shedding cuts costs

Today's chemical process plants use a combination of dedicated boilers, process-waste-heat boilers, and let-down devices to generate their steam needs. While this is more cost effective than using only dedicated boilers, it is difficult to guarantee that critical equipment will be provided with steam if one of these boilers fails. For instance, the sources of fuel for the boilers may fluctuate between oil, natural gas and process waste. As a plant's production changes, it waste-heat boiler loads also vary, as do the overall steam load and the availability of various fuels. This widely varying set of conditions increases the risk of upsetting or shutting down a plant's steam-distribution system. In case of an emergency, a scheme to selectively cut off steam to some production areas can reduce a plant's overall steam load sufficiently to ensure that steam is provided to those processes that are the most difficult and costly to start up. In the right circumstances, such as selective steam-load-shedding systems can provide major cost savings to plants. For example, an automated system in a major chemical and polymer plant in the Gulf Coast area saved $650,000 in maintenance, materials and overtimes charges the very first time steam load sheddingmore » was required. A steam-sensitive polymer process was completely protected, and the overhaul and startup costs of the affected production areas were minimized. Because most steam distribution systems and the logic for controlling them is very complex, it is explained with an example.« less